Work String Controller

ABSTRACT

Well bore servicing equipment is provided. The well bore servicing equipment comprises a first manipulator to grip a well bore work string, to raise the work string, and to lower the work string. The well bore servicing equipment further comprises a controller to receive a work string trajectory input and to automatically control the first manipulator to raise and lower the work string substantially in conformance with the work string trajectory input.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a Continuation Application of U.S. patent application Ser. No.12/140,191, filed Jun. 16, 2008 and published as US 2009/0308603 A1, andentitled “Work String Controller,” which is hereby incorporated byreference herein in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

REFERENCE TO A MICROFICHE APPENDIX

Not applicable.

BACKGROUND

Automated control systems attempt to drive physical characteristics of asystem, for example a process or object, to achieve system objectives.Automated control systems may be able to improve on the control providedmanually by a human operator, for example by providing a higherfrequency response, by taking account of a greater number of systemparameters, and/or by providing a higher accuracy of control. Automatedcontrol systems may take many forms and may be designed to usecontinuous time controllers and/or discrete time controllers. Controlsystems may be both designed and described with control diagramsrepresenting processing blocks. Generally, a control system may be builtand implemented from the control system diagram.

A well bore may be serviced using a work string. A work string mayinclude continuous coiled tubing which is fed continuously into the wellbore from large spools. The longer the continuous tubing, the greaterthe tensile strength of the tubing may be to support the weight of thelonger tubing. On the other hand, the greater the tensile strength ofthe tubing, the less flexible the tubing may be and the greater stressthat may be produced in the tubing as it flexes going into the well boreand coming back out of the well bore. An advantage of coiled tubing isthat it can be fed relatively rapidly and continuously into a well bore.A work string may also be composed of interconnected pieces or joints ofpipe, for example joints of pipe about 10 meters long with a malethreaded end and an opposite female threaded end. The pipe joints areconnected together by threading two pipe joints together tightly.Various tools may be attached to the end of the work string—eithercoiled tubing or interconnected joints of pipe—to accomplish a varietyof well bore operations.

SUMMARY

Disclosed herein is a well bore servicing equipment, comprising a firstmanipulator to grip a well bore work string, to raise the work string,and to lower the work string; and a controller to receive a work stringtrajectory input and to automatically control the first manipulator toraise and to lower the work string substantially in conformance with thework string trajectory input. The work string trajectory input maycomprise at least a work string target position and a work string targetvelocity. The work string trajectory input may comprise an orderedsequence of target pairs, wherein each target pair comprises a workstring target position and a work string target velocity, and whereinthe controller controls the first manipulator to drive the work stringto each of the work string target positions at the associated workstring target velocity with the work string target position in theordered sequence. The first manipulator may comprise a first slip bowlto grip the work string and a first hydraulic actuator to exert force onthe work string via the first slip bowl to raise and to lower the workstring. The first manipulator may further comprise a hydraulic axialpiston pump, and the controller may be operable to control the flow rateof the hydraulic axial piston pump, whereby the controller controls inpart the first manipulator. The first manipulator may further comprise asecond hydraulic actuator to exert force on the work string via thefirst slip bowl to raise and to lower the work string and a firsttraveling head that couples the first slip bowl to the first hydraulicactuator and to the second hydraulic actuator. The well bore servicingequipment may further include a second manipulator to grip the well borework string, to raise the work string, and to lower the work string, andthe controller may further automatically control the second manipulatorto raise and to lower the work string substantially in conformance withthe work string trajectory input. The well bore servicing equipment mayfurther include a collar detector to detect a collar location of thework string. The controller may coordinate control of the firstmanipulator and the second manipulator to provide substantiallycontinuous movement of the work string in accordance with the workstring trajectory input and to avoid one of the first manipulator andthe second manipulator gripping the work string at the collar locationof the work string, whereby increased operational speed is achieved. Thecontroller may comprise a first manipulator controller to provide afirst manipulator force command based on a feedback associated with thefirst manipulator, based on a model of the first manipulator, and basedon a first manipulator command trajectory that is based on the workstring trajectory input. The first manipulator may comprise an actuator,and the controller may comprise a first drive modulator to map a firstmanipulator force command and a first manipulator velocity command to anactuator control signal. The first drive modulator may map the firstmanipulator force command and the first manipulator velocity command tothe actuator control signal based on feedback associated with theactuator and based on a model of the actuator. The first manipulator maycomprise an actuator, and the controller may comprise a drive observerthat provides an estimated actuator parameter feedback value that issmoothed and substantially zero time lagged based on sensor informationreceived from the actuator, wherein the controller automaticallycontrols the first manipulator based in part on the estimated actuatorparameter feedback value. The actuator may be a hydraulic actuator, andthe drive observer system may provide the estimated hydraulic pressureparameter feedback value of a hydraulic chamber of the hydraulicactuator based in part on a model of the hydraulic actuator. The modelmay be based on an estimated effective piston area, an estimatedhydraulic fluid bulk modulus, and an estimated variable hydraulicchamber volume. The first manipulator may comprise a hydraulic actuator,and the controller may comprise a drive observer that provides anestimated flow disturbance value that is smoothed and based on sensorinformation received from the actuator, wherein the controllerautomatically controls the first manipulator based on the estimated flowdisturbance value. The first manipulator may comprise an actuator, andthe controller may comprise a manipulator observer that provides anestimated actuator position feedback value that is smoothed andsubstantially zero time lagged based on actuator position sensorinformation received from the actuator, wherein the controllerautomatically controls the first manipulator based in part on theestimated actuator position feedback value. The manipulator observerfurther may provide an estimated actuator velocity feedback value thatis smoothed and substantially zero time lagged based on actuatorvelocity sensor information received from the actuator, wherein thecontroller automatically controls the first manipulator based in part onthe estimated actuator velocity feedback value. The manipulator maycomprise a force coupling component to couple force output by theactuator to the work string, and the manipulator observer may providethe estimated actuator position feedback value based in part on a modelof the force coupling component. The model may be based on an estimatedmass of the force coupling component, an estimated weight of the forcecoupling component, and an estimated damping factor of the forcecoupling component. The model further may be based on an estimatedfriction of the force coupling component moving within a restraintmechanism. The first manipulator may comprise an actuator, and thecontroller may comprise a manipulator observer that provides anestimated disturbance force feedback value that is smoothed and based onactuator position sensor information received from the actuator, whereinthe controller may automatically control the first manipulator based inpart on the estimated disturbance force feedback value.

Further disclosed herein is a method of servicing a well bore with awork string, comprising receiving a control mode input identifying awork string control mode of operation; receiving a work stringtrajectory input; and automatically controlling a plurality ofmanipulators to drive the work string to substantially match the workstring trajectory input according to the work string control mode ofoperation. The work string control mode of operation may be a high speedsequential mode in which two manipulators are automatically controlled,and the method of servicing the well bore with the work string mayfurther comprise gripping the work string with a first manipulator;releasing the work string with a second manipulator; moving the workstring with the first manipulator; repositioning the second manipulator;first stopping the work string; then gripping the work string with thesecond manipulator; releasing the work string with the firstmanipulator; moving the work string with the second manipulator; andrepositioning the first manipulator. The work string control mode ofoperation may be a high speed sequential mode with stationary slipusage, and the method of servicing the well bore with the work stringmay further comprise gripping the work string with a stationary slipbowl before gripping the work string with the first manipulator;releasing the work string with the stationary slip bowl before movingthe work string with the first manipulator; gripping the work stringwith the stationary slip bowl before gripping the work string with thesecond manipulator; and releasing the work string with the stationaryslip bowl before moving the work string with the second manipulator. Thework string control mode of operation may be a high speed continuousmode in which two manipulators are automatically controlled, and themethod of servicing the well bore with the work string may furthercomprise gripping the work string with a first manipulator, withoutstopping the work string; releasing the work string with a secondmanipulator; moving the work string with the first manipulator;repositioning the second manipulator; gripping the work string with thesecond manipulator, without stopping the work string; releasing the workstring with the first manipulator; moving the work string with thesecond manipulator; and repositioning the first manipulator, wherein thework string may be moved by the manipulators to achieve at least one ofa substantially constant velocity and a substantially constantacceleration identified by the work string trajectory input. The workstring control mode of operation may be a high speed constrained mode inwhich two manipulators are automatically controlled, and the method ofservicing the well bore with the work string may further comprisegripping the work string with a first manipulator, without stopping thework string; releasing the work string with a second manipulator; movingthe work string with the first manipulator; repositioning the secondmanipulator; gripping the work string with the second manipulator,without stopping the work string; releasing the work string with thefirst manipulator; moving the work string with the second manipulator;and repositioning the first manipulator, wherein the work string may bemoved by the manipulators to remain within one or more operationalconstraints including a maximum mechanical load, a maximum electricalload, and a safety operational limit. The work string control mode ofoperation may be a high capacity sequential mode in which twomanipulators and a stationary slip bowl are automatically controlled,and the method of servicing the well bore with the work string mayfurther comprise gripping the work string with a first manipulator and asecond manipulator; releasing the work string with a stationary slipbowl; moving the work string with the first and second manipulator;stopping the work string with the first and second manipulator; grippingthe work string with the stationary slip bowl; releasing the work stringwith the first manipulator and the second manipulator; and repositioningthe first manipulator and the second manipulator. The work stringcontrol mode of operation may be a high capacity continuous mode inwhich at least three manipulators are automatically controlled, and themethod of servicing the well bore with the work string may furthercomprise gripping the work string with a first manipulator and a secondmanipulator; releasing the work string with a third manipulator; movingthe work string with the first and second manipulator; repositioning thethird manipulator; gripping the work string with the third manipulator;releasing the work string with the first manipulator; moving the workstring with the second and third manipulator; repositioning the firstmanipulator; gripping the work string with the first manipulator;releasing the work string with the second manipulator; moving the workstring with the first and third manipulator; and repositioning thesecond manipulator, wherein the work string is moved by the manipulatorsto achieve at least one of a substantially constant velocity and asubstantially constant acceleration identified by the work stringtrajectory input. In an embodiment, the plurality of manipulators maycomprise a dual-jacking system, wherein the dual-jacking systemcomprises a first pair of hydraulic actuators plumbed in parallel andcoupled to a first traveling head coupled to a first gripping device anda second pair of hydraulic actuators plumbed in parallel and coupled toa second traveling head coupled to a second gripping device. The workstring control mode of operation may be a high speed sequential mode,and the method of servicing the well bore with the work string mayfurther comprise gripping the work string with the first grippingdevice; releasing the work string with the second gripping device;moving the work string with the first pair of hydraulic actuators;repositioning the second pair of hydraulic actuators; first stopping thework string; gripping the work string with the second gripping device;releasing the work string with the first gripping device; moving thework string with the second pair of hydraulic actuators; andrepositioning the first pair of hydraulic actuators. The work stringcontrol mode of operation may be a high speed sequential mode withstationary slip usage, and the method of servicing the well bore withthe work string may further comprise gripping the work string with astationary slip bowl before gripping the work string with the firstgripping device; releasing the work string with the stationary slip bowlbefore moving the work string with the first pair of hydraulicactuators; gripping the work string with the stationary slip bowl beforegripping the work string with the second gripping device; and releasingthe work string with the stationary slip bowl before moving the workstring with the second pair of hydraulic actuators. The work stringcontrol mode of operation may be a high speed continuous mode, and themethod of servicing the well bore with a work string may furthercomprise gripping the work string with the first gripping device,without stopping the work string; releasing the work string with thesecond gripping device; moving the work string with the first pair ofhydraulic actuators; repositioning the second pair of hydraulicactuators; gripping the work string with the second gripping device,without stopping the work string; releasing the work string with thefirst gripping device; moving the work string with the second pair ofhydraulic actuators; and repositioning the first pair of hydraulicactuators, wherein the work string is moved by the dual-jacking systemto achieve at least one of a substantially constant velocity and asubstantially constant acceleration identified by the work stringtrajectory input. The work string control mode of operation may be ahigh speed constrained mode, and the method of servicing a well borewith a work string may further comprise gripping the work string withthe first gripping device, without stopping the work string; releasingthe work string with the second gripping device; moving the work stringwith the first pair of hydraulic actuators; repositioning the secondpair of hydraulic actuators; gripping the work string with the secondgripping device, without stopping the work string; releasing the workstring with the first gripping device; moving the work string with thesecond pair of hydraulic actuators; and repositioning the first pair ofhydraulic actuators, wherein the work string is moved by thedual-jacking system to remain within one or more operational constraintsincluding a maximum mechanical load, a maximum electrical load, and asafety operational limit. The work string control mode of operation maybe a high capacity sequential mode in which a stationary slip bowl isautomatically controlled, and the method of servicing the well bore withthe work string may further comprise gripping the work string with thefirst gripping device and the second gripping device; releasing the workstring with a stationary slip bowl; moving the work string with thefirst pair of hydraulic actuators and the second pair of hydraulicactuators; stopping the work string with the first pair of hydraulicactuators and the second pair of hydraulic actuators; gripping the workstring with the stationary slip bowl; releasing the work string with thefirst gripping device and the second gripping device; and repositioningthe first pair of hydraulic actuators and the second pair of hydraulicactuators.

Further disclosed herein is a control system comprising a firsthydraulic actuator having a rod side chamber and a piston side chamber;a hydraulic pump to provide hydraulic fluid at an adjustable pressureand an adjustable flow rate to the first hydraulic actuator; a firsthydraulic pressure sensor to produce an indication of a first hydraulicpressure of the hydraulic actuator; and a force modulator toautomatically control the flow rate of the hydraulic pump based on afirst force command, based on a first velocity command, and based on theindication of the first hydraulic pressure. The control system mayfurther comprise a directional flow control valve coupled to the firsthydraulic actuator and to the hydraulic pump and operable to becommanded to direct hydraulic fluid from the hydraulic pump to one ofthe rod side chamber of the hydraulic actuator, the piston side chamberof the hydraulic actuator, or to a return port of the hydraulic pump,and the force modulator further automatically commands the directionalflow control valve based on the first force command, based on the firstvelocity command, and based on the indication of the hydraulic pressurefrom the first pressure sensor, whereby the direction of force producedby the hydraulic actuator is controlled. The first hydraulic pressuremay be a hydraulic pressure of the rod side chamber, and the controlsystem may further comprise a second pressure sensor to produce anindication of a hydraulic pressure of the piston side chamber; and apressure observer to produce an estimate of the hydraulic pressure ofthe rod side chamber based on the indication of the hydraulic pressureof the rod side chamber produced by the first hydraulic pressure sensorand to produce an estimate of the hydraulic pressure of the piston sidechamber based on the indication of the hydraulic pressure of the pistonside chamber produced by the second pressure sensor, and the forcemodulator may automatically control the flow rate of the hydraulic pumpbased at least in part on the estimate of the hydraulic pressure of therod side chamber and on the estimate of the hydraulic pressure of thepiston side chamber. The control system may further comprise a positionsensor, coupled to the first hydraulic actuator, to produce anindication of the position of a rod end of the first hydraulic actuatorand a velocity sensor, coupled to the first hydraulic actuator, toproduce an indication of the velocity of the rod end of the firsthydraulic actuator, wherein the manipulator controller may furtherdetermine the first force command at least in part based on theindication of the position of the rod end of the first hydraulicactuator and on the indication of the velocity of the rod end of thefirst hydraulic actuator. The control system may further comprise aposition and velocity observer to produce an estimate of the position ofthe first hydraulic actuator based on the indication of the position ofthe rod end of the first hydraulic actuator and to produce an estimateof the velocity of the rod end of the first hydraulic actuator based onthe indication of the velocity of the rod end of the first hydraulicactuator, wherein the manipulator controller may transmit the firstforce command to the force modulator based at least in part on theestimate of the position of the rod end of the first hydraulic actuatorand on the estimate of the velocity of the rod end of the firsthydraulic actuator. The control system may further comprise a flowregulator to produce a hydraulic pump control signal under the controlof the force modulator, whereby the force modulator controls the flowrate of the hydraulic pump through the flow regulator.

Further disclosed herein is an automated hydraulic flow regulator,comprising a proportional-integral (PI) controller portion to determinea flow error and to generate a corrective signal based on the flowerror; a command feed-forward portion to determine a commandfeed-forward signal based on a flow rate command and an estimate of ahydraulic pump motor angular velocity; and a pump control gain toamplify the sum of the corrective signal and the command feed-forwardsignal to produce a commanded hydraulic pump motor signal, whereby theautomated hydraulic flow regulator controls a hydraulic flow. The flowerror may be determined as the difference of the flow rate command and asensed flow rate. The command feed-forward signal may be determined byamplifying the flow rate command by a feed-forward gain, wherein thefeed-forward gain may be inversely proportional to the estimate of thehydraulic pump motor angular velocity. The hydraulic flow regulator mayfurther include an axial piston pump that produces the hydraulic flow,wherein the commanded hydraulic pump motor signal controls the axialpiston pump by controlling the angular displacement of a swash plate ofthe axial piston pump.

Further disclosed herein is an automated force modulator, comprising aproportional gain controller portion to determine a force error and togenerate a corrective signal based on the force error; a commandfeed-forward portion to determine a command-feed forward signal based ona velocity command and a directional area gain, wherein the directionalarea gain has a first value when the velocity command has a firstpolarity and the directional area gain has a second value when thevelocity command has a second polarity; and a summation junction tooutput a commanded flow signal based on the corrective signal and thecommand feed-forward signal. The force error may be determined as thedifference of a force command and an estimated force. The estimatedforce may be determined based on an indication of a rod side pressure ofa hydraulic actuator and a piston side pressure of the hydraulicactuator. The first value of directional area gain may be proportionalto the area of a piston of a hydraulic actuator, and the second value ofdirectional area gain may be proportional to the area of the piston ofthe hydraulic actuator minus the cross-section area of a rod of thehydraulic actuator. The summation junction may output the commanded flowsignal based further on a flow disturbance term. The automated forcemodulator may further comprise a directional valve modulator to output adirectional valve command based on the polarity of a sum of thecorrective signal and the command feed-forward signal.

Further disclosed herein is an automated manipulator controller,comprising a proportional-integral-derivative (PID) controller portionto determine a manipulator position error and a manipulator velocityerror and to generate a corrective signal based on the manipulatorposition error and the manipulator velocity error; a commandfeed-forward portion to determine a command feed-forward signal based ona manipulator acceleration command and a manipulator mass gain; amanipulator damping gain to determine a manipulator damping force basedon a manipulator damping gain and an indication of manipulator velocity;and a summation junction to output a first manipulator force commandbased on the corrective signal, the command feed-forward signal, themanipulator damping force, and a feed forward work string load command.The manipulator position error may be determined as the difference of amanipulator position command and an indication of manipulator position,and the manipulator velocity error may be determined as the differenceof a manipulator velocity command and the indication of manipulatorvelocity. The summation junction may further output the firstmanipulator force command based on a manipulator weight. The summationjunction may further output the first manipulator force command based ona difference between the manipulator force command and an estimate of amanipulator force disturbance.

Further disclosed herein is a pressure estimator comprising adirectional valve command feed forward component to produce a rod sideflow command and a piston side flow command based on a directional flowvalve command and a feed forward flow rate command; a piston sidepressure observer to produce an estimated piston side pressure based onthe piston side flow command, a sensed piston side pressure, an actuatorvelocity, and an actuator position; and a rod side pressure observer toproduce an estimated rod side pressure based on the rod side flowcommand, a sensed rod side pressure, the actuator velocity, and theactuator position. The pressure estimator may further comprise adirectional valve disturbance flow component to estimate a disturbanceflow based on the directional flow valve command, the estimated pistonside pressure, and the estimated rod side pressure. When the directionalflow valve command has a piston side value, the piston side flow commandmay be proportional to the feed forward flow rate command and the rodside flow command may be proportional to the negative value of the feedforward flow rate command. When the directional flow valve command has arod side value, the piston side flow command may be proportional to thenegative value of the feed forward flow rate command and the rod sideflow command may be proportional to the value of the feed forward flowrate command. When the directional flow valve command has a piston sidevalue, the rod side flow command further may be proportional to aneffective rod side area of the piston divided by the effective pistonside area of the piston. When the directional flow valve command has arod side value, the piston side flow command further may be proportionalto the effective piston side area of the piston divided by the effectiverod side area of the piston.

Further disclosed herein is a pressure observer comprising a firstproportional-integral (PI) controller portion to determine a firstpressure error and to generate a first corrective signal based on thefirst pressure error; a first feed-forward portion to determine a firstflow rate based on a velocity and a first gain; a first integrator tointegrate the sum of the first corrective signal and the first flowrate; and a second gain to amplify an output of the first integrator bya first model gain and to produce a first pressure estimate. The firstproportional-integral controller portion may further determine a firstflow disturbance signal based on the first pressure error. The firstpressure error may be determined as the difference of a first sensedpressure and the first pressure estimate. The first gain may beproportional to the difference of an area of a piston of a hydraulicactuator and a cross-section area of a rod of the hydraulic actuator.The first model gain may be proportional to a bulk modulus of ahydraulic fluid and may be inversely proportional to a volume comprisinga rod side chamber of a hydraulic actuator, wherein the volume of therod side chamber may change as a rod of the hydraulic actuator moves.The pressure observer may further comprise a secondproportional-integral (PI) controller portion to determine a secondpressure error and to generate a second corrective signal based on thesecond pressure error; a second feed-forward portion to determine asecond flow rate based on the velocity and a second gain; a secondintegrator to integrate the sum of the second corrective signal and thesecond flow rate; and a second gain to amplify an output of the secondintegrator by a second model gain and to produce a second pressureestimate.

Further disclosed herein is a manipulator position and velocity observercomprising a proportional-integral-derivative (PID) controller portionto determine a manipulator position error and a manipulator velocityerror and to generate a corrective signal based on the manipulatorposition error and on the manipulator velocity error; a first gain toamplify an indication of manipulator velocity by a manipulator dampergain to generate a damper force signal; a force summation portion thatis operable to determine a summed force term based on the correctivesignal, based on the damper force signal, based on a force command, andbased on a manipulator weight term; a second gain to amplify the summedforce term by an inverse manipulator gain and to generate a manipulatoracceleration term; a first integrator to integrate the manipulatoracceleration term to generate a manipulator velocity term and to outputan estimate of manipulator velocity; and a second integrator tointegrate the manipulator velocity term to generate a manipulatorposition term and to output an estimate of manipulator position. Theproportional-integral-derivative controller portion may be furtheroperable to produce a manipulator force disturbance term based on themanipulator position error and on the manipulator velocity error. Themanipulator position error may be determined as the difference of asensed manipulator position and the estimate of manipulator position,and the manipulator velocity error may be determined as the differenceof a sensed manipulator velocity and the estimate of manipulatorvelocity.

Further disclosed herein is a work string controller comprising a firstproportional-integral-derivative (PID) controller portion to determine afirst position error and a first velocity error and to generate a firstsimulated force feedback based on the first position error and the firstvelocity error; a second proportional-integral-derivative (PID)controller portion to determine a second position error and a secondvelocity error and to generate a second simulated force feedback basedon the second position error and the second velocity error; a thirdproportional-integral-derivative (PID) controller portion to determine awork string position error and a work string velocity error and togenerate a force term based on the work string position error, based onthe work string velocity error, based on the first simulated forcefeedback, and based on the second simulated force feedback; a gain toamplify the force term by a work string mass gain to produce anacceleration term; a first integrator to integrate the acceleration termto produce an estimated work string velocity; a second integrator tointegrate the estimated work string velocity term to produce anestimated work string position; and a commands generator to produce afirst slip bowl command, a first acceleration command, a first velocitycommand, a first position command, a second slip bowl command, a secondacceleration command, a second velocity command, and a second positioncommand based on the estimated work string velocity and the estimatedwork string position. The commands generator may be further operable toproduce the first and second slip bowl commands based on a collarindication. The work string mass gain may be inversely proportional to amass of a work string. The work string controller may further comprise afirst slip bowl portion to determine a first slip bowl error based on afirst estimated slip bowl position, a first commanded slip bowlposition, and a first slip bowl model; a first proportional-integral(PI) controller portion to generate a third simulated force feedbackbased on the first slip bowl error; a second slip bowl portion todetermine a second slip bowl error based on a second estimated slip bowlposition, a second commanded slip bowl position, and a second slip bowlmodel; and a second proportional-integral (PI) controller portion togenerate a fourth simulated force feedback based on the second slip bowlerror, wherein the third proportional-integral-derivative controllerportion generates the force term further based on the third simulatedforce feedback and the fourth simulated force feedback.

Further disclosed herein is a collar locator, comprising a first digitalcamera to capture a first image; and a collar detector coupled to thefirst digital camera and operable to generate a first thresholded imageof the first image, to generate a first edge detection analysis of thefirst thresholded image, and to determine the location of a collar basedin part on the first edge detection analysis. The collar locator mayfurther include a first light source, whereby the light source mayilluminate a work string that is at least a portion of the first image.The collar locator may further comprise a second digital camera tocapture a second image, wherein the collar detector is coupled to thesecond digital camera, and the collar locator may further generate asecond thresholded image of the second image, generate a second edgedetection analysis of the second thresholded image, and determine thelocation of the collar based in part on the second edge detectionanalysis. In an embodiment, the first and second digital cameras mayeach capture a plurality of images at a periodic rate, and the collardetector may determine a position and a velocity of the collar based onthe plurality of images. In an embodiment, the first and second digitalcameras may each capture about 30 images per second.

Further disclosed herein is a method of servicing a well bore with awork string comprising placing the work string in a well bore; receivinga work string trajectory input; determining a simulated force feedbackof the work string on a first manipulator; determining an estimated workstring velocity based at least on the simulated force feedback of thework string on the first manipulator; determining an estimated workstring position based at least on the simulated force feedback of thework string on the first manipulator; determining a first manipulatorposition command and a first manipulator velocity command based on theestimated work string position and the estimated work string velocity;and automatically controlling the first manipulator based at least onthe first manipulator position command and the first manipulatorvelocity command. Determining the estimated work string velocity maycomprise determining a corrective signal based on a work string positioncommand and a work string velocity command, combining the simulatedforce feedback of the work string on the at least one manipulator andthe corrective signal to determine a force term, converting the forceterm to an acceleration term, and integrating the acceleration term todetermine the simulated work string velocity. Determining the estimatedwork string position may comprise integrating the estimated work stringvelocity to determine the simulated work string position. The simulatedforce feedback of the work string on the at least one manipulator may bedetermined as the sum of a plurality of a simulated force feedback ofthe work string on a manipulator, and determining the simulated forcefeedback of the work string on the manipulator may comprise determininga manipulator position error term, determining a manipulator velocityerror term, amplifying the manipulator position error term to produce afirst proportional term, integrating and amplifying the manipulatorposition error term to produce a first integral term, amplifying thevelocity error term to produce a first derivative term, and summing thefirst proportional term, the first integral term, and the firstderivative term. In an embodiment, determining the simulated forcefeedback of the work string on the manipulator may further comprisedetermining a slip bowl position error, amplifying the slip bowlposition error by a second proportional gain to produce a secondproportional term, integrating and amplifying the slip bowl positionerror to produce a second integral term, and summing the secondproportional term, the second integral term, the first proportionalterm, the first integral term, and the first derivative term. In anembodiment, the first integral gain may be used to produce the firstintegral term, and a second integral gain may be used to produce thesecond integral term, wherein the second integral gain may be at leastabout ten times larger than the first integral gain. Controlling thefirst manipulator may be further based on a collar indication input.Controlling the work string may further include determining a secondmanipulator position command and a second manipulator velocity commandbased on the simulated force feedback of the work string on the at leastone manipulator, the estimated work string position, the estimated workstring velocity, and the work string trajectory input; and automaticallycontrolling a second manipulator based on the second manipulatorposition command and the second manipulator velocity command. The methodmay further comprise determining a simulated force feedback of the workstring on an a second manipulator; determining the estimated work stringvelocity further based on the simulated force feedback of the workstring on the second manipulator; determining the estimated work stringposition further based on the simulated force feedback of the workstring on the second manipulator; determining a first feed forward workstring load command, a second manipulator position command, a secondmanipulator velocity command, and a second feed forward work string loadcommand based on the estimated work string position and the estimatedwork string velocity; further automatically controlling the firstmanipulator based on the first feed forward work string load command;and automatically controlling the second manpulator based at least onthe second manipulator position command, the second manipulator velocitycommand, and the second feed forward work string load command.

These and other features will be more clearly understood from thefollowing detailed description taken in conjunction with theaccompanying drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure, referenceis now made to the following brief description, taken in connection withthe accompanying drawings and detailed description, wherein likereference numerals represent like parts.

FIG. 1 is a block diagram of a control system according to someembodiments of the disclosure.

FIG. 2A is an illustration of a single actuator hydraulic power systemaccording to some embodiments of the disclosure.

FIG. 2B is an illustration of a two actuator hydraulic power systemaccording to other embodiments of the disclosure.

FIG. 3 is an illustration of a dual-jacking mechanism according to someembodiments of the disclosure.

FIG. 4 is a block diagram of a work string control system according tosome embodiments of the disclosure.

FIG. 5 is an illustration of a feedback vector according to someembodiments of the disclosure.

FIG. 6 is a block diagram of a manipulator control system and amanipulator physical system interface according to some embodiments ofthe disclosure.

FIG. 7 is control diagram of a flow regulator according to someembodiments of the disclosure.

FIG. 8 is a control diagram of a force modulator according to someembodiments of the disclosure.

FIG. 9 is a control diagram of a traveling head controller according tosome embodiments of the disclosure.

FIG. 10 is a block diagram of a drive observer according to someembodiments of the disclosure.

FIG. 11 is a control diagram of a rod side pressure observer and apiston side pressure observer according to some embodiments of thedisclosure.

FIG. 12 is a control diagram of a traveling head position and velocityobserver according to some embodiments of the disclosure.

FIG. 13 is a block diagram of a work string controller according to someembodiments of the disclosure.

FIG. 14 is a control diagram of a manipulator simulated force feedbackcomponent according to an embodiment of the disclosure.

FIG. 15 is an illustration of a kinematic model according to anembodiment of the disclosure.

FIG. 16 is an illustration of a pipe collar locator according to anembodiment of the disclosure.

FIG. 17 is a flow chart of a method of controlling a work stringaccording to an embodiment of the disclosure.

FIG. 18 illustrates an exemplary general purpose computer systemsuitable for implementing the several embodiments of the disclosure.

DETAILED DESCRIPTION

It should be understood at the outset that although illustrativeimplementations of one or more embodiments are illustrated below, thedisclosed systems and methods may be implemented using any number oftechniques, whether currently known or in existence. The disclosureshould in no way be limited to the illustrative implementations,drawings, and techniques illustrated below, but may be modified withinthe scope of the appended claims along with their full scope ofequivalents.

In the figures and in the text herein below, variable names and variablesymbols that are associated with an asterisk, for example F*, generallyrepresent commanded values. Variable names and variable symbols that areassociated with a caret, for example F̂, generally represent estimatedvalues. Variable names and variable symbols that are not associated withany additional symbol, for example F, generally represent measuredand/or actual values. Turning now to FIG. 1, a control systemarchitecture 8 suitable for some of the embodiments of the presentdisclosure is discussed. The control system architecture 8 includes asystem controller 10, a plurality of manipulator controllers 20, amanipulator observer system 30, a plurality of drive modulators 40, adrive observer system 50, a plurality of manipulator physical systems60, and a manipulated physical system 70. An embodiment of the systemcontroller 10 is shown in FIG. 13 and described in more detailhereinafter. An embodiment of the manipulator controller 20 is shown inFIG. 9 and described in more detail hereinafter. An embodiment of themanipulator observer system 30 is shown in FIG. 12 and described in moredetail hereinafter. An embodiment of the drive modulator 40 is shown inFIG. 7 and FIG. 8 and described in more detail hereinafter. Anembodiment of the drive observer system 50 is shown in FIG. 10 and FIG.11 and described in more detail hereinafter. An embodiment of themanipulator physical system 60 is shown in FIG. 2A, FIG. 2B, FIG. 3,FIG. 6, and FIG. 7 and described in more detail hereinafter. Anembodiment of the manipulated physical system 70 is shown in FIG. 3 andFIG. 16 and discussed in more detail hereinafter.

While FIG. 1 depicts three separate manipulator systems 60, in differentembodiments, different numbers of manipulators 60, drive modulators 40,and manipulator controllers 20 may be implemented. Also, while FIG. 1depicts a second manipulator physical system 60-b, a second drivemodulator 40-b, and a second manipulator controller 20-b as well as athird manipulator physical system 60-c, a third drive modulator 40-c,and a third manipulator controller 20-c without an associatedmanipulator observer system 30 and without an associated drive observersystem 50, in other embodiments a manipulator observer system 30 and/ora drive observer system 50 may be associated with these system controlcomponents. The system controller 10 receives a system controllercommand signal 12, a physical system feedback 16 from the manipulatedphysical system 70, and a manipulator feedback 14 from each of themanipulator physical systems 60 as input, for example a firstmanipulator feedback 14-a from the first manipulator physical system60-a, a second manipulator feedback 14-b from the second manipulatorphysical system 60-b, and a third manipulator feedback 14-c from thethird manipulator physical system 60-c. In an embodiment, the systemcontroller command signal 12 may comprise a work string trajectoryinput. The system controller 10 outputs a manipulator controller commandsignal 22 to each of the manipulator controllers 20. In an embodiment,the manipulator controller command signal 22 may comprise a manipulatorcommand trajectory that is based on a work string trajectory input tothe system controller 10. In an embodiment, a first manipulatorcontroller command signal 22-a may comprise a first manipulator commandtrajectory and a second manipulator controller command signal 22-b maycomprise a second manipulator command trajectory, wherein both the firstmanipulator command trajectory and the second manipulator commandtrajectory are based on the work string trajectory input. The generalpurpose of the control system architecture 8 is to drive the physicalsystem 70 according to the system controller command signal 12. In anembodiment, the system controller command signal 12 may be a trajectorydescribing the position, velocity, and acceleration of the manipulatedphysical system 70 at different times. The system controller commandsignal 12 may further include various mode and commands. In anembodiment, the control system architecture 8 comprises well boreservicing equipment, for example a control system automaticallycontrolling a plurality of manipulators to raise and lower a well borework string in and out of a well bore to accomplish a well boreservicing job.

Each of the manipulator controllers 20 receives a manipulator controllercommand signal 22 from the system controller 10 and one of a manipulatorobserver feedback signal 34 from the manipulator observer system 30 or amanipulator feedback 24 as inputs. Each of the manipulator controllers20 outputs a drive modulator command signal 42 to the drive modulator40. The first manipulator controller 20-a also outputs a firstmanipulator controller output signal 32 to the manipulator observersystem 30. With respect to describing FIG. 1, the term “signal” may meaneither a single signal or a vector of signals. For example, in anembodiment, the command signal 22 may comprise a commanded travelinghead position signal, a commanded traveling head velocity signal, acommanded traveling head acceleration signal, a commanded traveling headforce signal, and a commanded slip bowl position signal.

Each of the drive modulators 40 receives the drive modulator commandsignal 42 from the manipulator controller 20 and a manipulator feedbacksignal 44 from the manipulator physical system 60. The first drivemodulator 40-a also receives a first drive observer system output signal58 from the first drive observer system 50. Each of the drive modulators40 outputs a manipulator physical system command signal 62 to themanipulator physical system 60. The first drive modulator 40-a alsooutputs a first drive modulator output signal 52 to the first driveobserver system 50.

The manipulator observer system 30 receives the first manipulatorcontroller output signal 32 and a first manipulator feedback 24-a. Themanipulator observer system 30 outputs the first manipulator observerfeedback signal 34 to the first manipulator controller 20-a and a firstmanipulator observer system output signal 54 to the first drive observersystem 50.

The first drive observer system 50 receives the first observer outputsignal 54 from the manipulator observer system 30, the first drivemodulator output signal 52 from the first drive modulator 40-a, and afirst manipulator feedback signal 56 from the first manipulator physicalsystem 60-a. The first drive observer system 50 outputs the first driveobserver system output signal 58 to the first drive modulator 40-a.

Each of the manipulator physical systems 60 receives the manipulatorphysical system command signal 62 from the drive modulator 40. Each ofthe manipulator physical systems 60 outputs a plurality of feedbacksignals 14, 24, and 44 to the system controller 10, the manipulatorobserver system 30 or the manipulator controller 20, and the drivemodulator 40, respectively. Additionally, the first manipulator physicalsystem 60-a outputs a first manipulator feedback signal to the firstdrive observer system 50. Each of the manipulator physical systems 60also interacts with the manipulated physical system 70, represented inFIG. 1 by the manipulated physical system interaction with manipulator72. For example, in an embodiment, the manipulated physical system 70may be a work string for servicing and/or drilling a well bore and themanipulators 60 may be a plurality of hydraulic jacks coupled to slipbowls configured to grip the work string. The work string may comprise aplurality of connected segments (e.g., drill string, tubing string,casing string, etc.) or a continuous length of oilfield tubular such ascoiled tubing. The work string may have one or more associated orconnected tools, for example one or more down hole tools positioned ator near a terminal end of the work string. In some embodiments, theseveral manipulator physical systems 60 that manipulate the manipulatedsystem 70 may be of different types. The manipulator physical system 60may include hydraulic actuators, electric motor actuated screw jacks,robot lever arms, slip bowls, and other devices. In another embodiment,the manipulated physical system 70 may be some other object manipulatedby one or more manipulator physical systems 60 that are robotic arms. Itshould be understood that the control system architecture 8 depicted inFIG. 1 is suitable to a number of alterations, modifications, andarrangements of components, all of which are contemplated by the presentdisclosure.

Turning now to FIG. 2A, a single actuator hydraulic system 100 isdescribed. The single actuator hydraulic system 100 comprises ahydraulic pump 102, a directional flow valve 104, a hydraulic pressuresupply line 106, a hydraulic return line 107, a hydraulic fluidreservoir 108, a hydraulic supply line 109, a hydraulic actuator 110, arod side hydraulic line 112, a piston side hydraulic line 114, a firstcounterbalance valve 115-a, and a second counterbalance valve 115-b. Inan embodiment, the hydraulic pump 102 provides pressurized flow ofhydraulic fluid at an effective pressure and rate of flow to drive thehydraulic actuator 110 according to operational control regimes. Indifferent embodiments, different hydraulic pumps 102 may be selected toprovide different flow/pressure capacities and/or different pumpratings. Pressurized hydraulic fluid flows through the hydraulicpressure supply line 106 to the hydraulic actuator 110 under the controlof the directional flow valve 104. The hydraulic fluid is returned fromthe hydraulic actuator 110 through the hydraulic return line 107 tohydraulic fluid reservoir 108 under the control of the directional flowvalve 104. The hydraulic pump 102 draws hydraulic fluid from thehydraulic fluid reservoir 108 via the hydraulic supply line 109. Thedirectional flow valve 104 directs pressurized hydraulic fluid to therod side hydraulic line 112 when in a first control state, to the pistonside hydraulic line 114 when in a second state, and to the hydraulicreturn line 107 when in a third state.

In an embodiment, the directional flow valve 104 has four ports whichconnect to the hydraulic pressure supply line 106, the hydraulic returnline 107, the rod side hydraulic line 112, and the piston side hydraulicline 114. The directional flow valve 104 has an internal diverting spoolthat is electrically actuated by use of a first and a second solenoid.When the first solenoid is energized, the internal diverting spool isdisplaced to a first position, connecting the hydraulic pressure supplyline 106 with the rod side hydraulic line 112 and connecting thehydraulic return line 107 with the piston side hydraulic line 114. Whenthe second solenoid is energized, the internal diverting spool isdisplaced to a second position, connecting the hydraulic pressure supplyline 106 to the piston side hydraulic line 114 and the hydraulic returnline 107 to the rod side hydraulic line 112. When neither the firstsolenoid or the second solenoid is energized, the internal divertingspool remains in a neutral position, and all four hydraulic lines—thehydraulic pressure supply line 106, the hydraulic return line 107, therod side hydraulic line 112, and the piston side hydraulic line 114—areconnected together, effectively routing the hydraulic pressure supplyline 106 to the hydraulic return line 107 and bypassing both the rodside hydraulic line 112 and the piston side hydraulic line 114.

The hydraulic actuator 110 comprises a rod 116 attached to a piston 118.The rod 116 is supported and retained by an end cap (not shown) of thehydraulic actuator 110 and by the piston 118. The piston 118 issupported by the interior of the hydraulic actuator 110. The rod 116 maybe coupled to a weight bearing structure (not shown) to manipulate ormove the weight bearing structure. The interior of the hydraulicactuator 110 includes a rod side chamber 120 and a piston side chamber122. By directing hydraulic fluid at different pressures into the rodside chamber 120 from the rod side hydraulic line 112 and into thepiston side chamber 122 from the piston side hydraulic line 114, the rod116 is driven under force in different directions. The force exerted bythe rod 116 may be calculated to be the difference of the product of anarea of the piston 118 multiplied by the hydraulic pressure, P_(PS), inthe piston side chamber 122 and a product of the hydraulic pressure,P_(RS), in the rod side chamber 120 multipled by an area determined asthe area of the piston 118 minus a cross-sectional area of the rod 116.In different embodiments, different hydraulic actuators 110 may beselected having different stroke lengths, different diameters, differentpiston sizes, different chamber volumes, and other differentspecifications, capacities, and/or dimensions.

In an embodiment, a first counterbalance valve 115-a is installed in therod side hydraulic line 112 and a second counterbalance valve 115-b isinstalled in the piston side hydraulic line 114. The first and secondcounterbalance valves 115-a, b are cross-connected to each other. Thepurpose of the first and second counterbalance valves 115-a, b is tohold any overrunning loads of the hydraulic actuator 110. For example,if the hydraulic actuator 110 is extended and bearing a heavy weight, asmay be the case when the hydraulic actuator 110 is supporting a longpipe string or coiled tubing, and then the single actuator hydraulicsystem 100 is controlled or commanded to direct hydraulic fluid andpressure to the rod side chamber 120 and to return hydraulic fluid fromthe piston side chamber 122, while not choking back the flow out of thepiston side chamber 122, the hydraulic actuator 110 and the load itsupports may fall uncontrolled at the rate which the hydraulic fluid canescape the piston side chamber 122. The first and second counterbalancevalves 115-a, b promote maintaining controlled movement of the hydraulicactuator 110 by holding back hydraulic fluid so that the hydraulicactuator 110 does not run away or fall.

The first counterbalance valve 115-a provides a first pilot hydraulicpressure to the second counterbalance valve 115-b, and, similarly, thesecond counterbalance valve 115-b provides a second pilot hydraulicpressure to the first counterbalance valve 115-a. In order to move thehydraulic actuator 110 in a manner that requires fluid to flow throughthe first counterbalance valve 115-a into the rod side chamber 120 andfor fluid to exit the piston side chamber 122 through the secondcounterbalance valve 115-b, sufficient hydraulic pressure must besupplied by the first pilot hydraulic pressure to the secondcounterbalance valve 115-b. Similarly, in order to move the hydraulicactuator 110 in a manner that requires fluid to flow through the secondcounterbalance valve 115-b into the piston side chamber 122 and forfluid to exit the rod side chamber 120 through the first counterbalancevalve 115-a, sufficient hydraulic pressure must be supplied by thesecond pilot hydraulic pressure to the first counterbalance valve 115-a.Counterbalance valves 115 may be employed in both the rod side hydraulicline 112 and the piston side hydraulic line 114, because the work stringmay be either heavily weighted and exerting a downwards force on thehydraulic actuator 110 or heavily buoyant and exerting an upwards forceon the hydraulic actuator 110. These conditions may be referred to aswork string heavy and work string light, respectively.

Turning now to FIG. 2B, a two actuator hydraulic system 130 isdescribed. The two actuator hydraulic system 130 is substantiallysimilar to the single actuator hydraulic system 100, with the differencebeing that the two actuator hydraulic system 130 contains two hydraulicactuators 110, a first hydraulic actuator 110-a and a second hydraulicactuator 110-b, plumbed in parallel. The first hydraulic actuator 110-acomprises a first rod 116-a attached to a first piston 118-a. Theinterior of the first hydraulic actuator 110-a includes a first rod sidechamber 120-a and a first piston side chamber 122-a. Similarly, thesecond hydraulic actuator 110-b comprises a second rod 116-b attached toa second piston 118-b. The interior of the second hydraulic actuator110-b includes a second rod side chamber 120-b and a second piston sidechamber 122-b. The two rod side chambers 120-a, b are plumbed inparallel from the common rod side hydraulic line 112, and the two pistonside chambers 122-a, b are plumbed in parallel from the common pistonside hydraulic line 114. Because the hydraulic actuators 110 are plumbedin parallel, the function of the directional flow valve 104 and thecounterbalance valves 115 remain the same as described with respect toFIG. 2A. The use of multiple hydraulic actuators 110, for example twohydraulic actuators 110-a, 110-b as illustrated in FIG. 2B, may provideincreased force to apply to a manipulated object. Additionally, the useof multiple hydraulic actuators 110 may promote ease of force transferfrom the hydraulic actuators 110 to the manipulated object or objects.

Turning now to FIG. 3, a dual-jacking system 150 is described. Thedual-jacking system 150 is operable to manipulate a work string 152 inand out of a well bore (not shown) to a target depth Z and at a targetvelocity V under automatic control of a work string controller to bedescribed hereinafter. The dual-jacking system 150 comprises a firstslip bowl 154, a first traveling head 156, a second slip bowl 158, asecond traveling head 160, and four hydraulic actuators—the firsthydraulic actuator 110-a, the second hydraulic actuator 110-b, a thirdhydraulic actuator 110-c, and a fourth hydraulic actuator 110-d. Thefirst hydraulic actuator 110-a and the second hydraulic actuator 110-bare coupled to opposite ends of the first traveling head 156. The thirdhydraulic actuator 110-c and the fourth hydraulic actuator 110-d arecoupled to opposite ends of the second traveling head 160. Thedual-jacking system 150 may also comprise a stationary slip bowl 162. Insome contexts, slip bowls may be referred to as grasping actuators thatmay be said to assume a non-grasping position when open and a graspingposition when closed. In an embodiment, the bases of the hydraulicactuators 110-a, b, c, d and the stationary slip bowl 162 may beattached to and supported by another structure, for example a drillingderrick, a work-over rig, or some other support structure. The positiveZ direction is oriented downwards, into a well bore (not shown). Thepositive V velocity is oriented downwards, into the well bore.

The two hydraulic actuators 110-c, d are substantially similar to thehydraulic actuators 110-a, b described above with reference to FIG. 2B.Because in some control regimes or operational modes the two hydraulicactuators 110-a, b and the two hydraulic actuators 110-c, d may becommanded independently, the two hydraulic actuators 110-a, b may becoupled to a first directional flow valve 104-a (not shown) and a firsthydraulic pump 102-a (not shown) and the two hydraulic actuators 110-c,d may be coupled to a second directional flow valve 104-b (not shown)and a second hydraulic pump 102-b (not shown).

By commanding the first slip bowl 154 to grip the work string 152 andcommanding the first hydraulic actuator 110-a and the second hydraulicactuator 110-b in unison, the work string 152 may be manipulated to movein and out of the well bore. In effect, the parallel plumbing of thefirst and second hydraulic actuators 110-a, b described above results inthe common motion of the first and second hydraulic actuators 110-a, b.Similarly, by commanding the second slip bowl 158 to grip the workstring 152 and commanding the third hydraulic actuator 110-c and thefourth hydraulic actuator 110-d in unison, the work string 152 may bemanipulated to move in and out of the well bore. Again, in effect, theparallel plumbing of the third and fourth hydraulic actuators 110-c, ddescribed above results in the common motion of the third and fourthhydraulic actuators 110-c, d. The stationary slip bowl 162 may becommanded to grip the work string 152 during different operation modes,for example during transfer of the load from the first slip bowl 154 tothe second slip bowl 158 and from the second slip bowl 158 to the firstslip bowl 154. During some operation modes, however, the stationary slipbowl 162 may not be employed. The four hydraulic actuators 110-a, b, c,d may move to about the extended limit of their travel and to about theretracted limit of their travel. In some embodiments, the first andsecond hydraulic actuators 110-a, b are about fully extended while thethird and fourth hydraulic actuators 110-c, d are about fully retracted,and vice-versa, that is the hydraulic actuator pairs may have aboutopposite traversal (e.g., opposite direction and velocity). In anembodiment, the motions of the four hydraulic actuators 110-a, b, c, dare guided by rails or other structures (not shown) that constrain theirmotions to substantially one axis of motion, for example positive andnegative Z-axis motion. For further details of the dual jacking system150, see U.S. Pat. No. 6,688,393 B2 issued Feb. 10, 2004, entitled DualJacking System and Method by Eric M. Sredensek and Michael S. Oser,which is hereby incorporated by reference for all purposes.

In one case, for example when the weight of the work string 152 ismoderate, the hydraulic actuators 110 may be commanded so that while thefirst slip bowl 154 grips the work string 152 and the first and secondhydraulic actuators 110-a, b move the work string 152 in a positive Zdirection, the second slip bowl 158 is disengaged from the work string152 and the third and fourth hydraulic actuators 110-c, d move in anegative Z direction. At about the limits of travel, the hydraulicactuators 110 are commanded to stop, bringing the work string 152, bothslip bowls 154, 158, and both traveling heads 156, 160 to a stop withzero velocity. The second slip bowl 158 is engaged to grip the workstring 152, and the first slip bowl 154 is disengaged from the workstring 152. This operation may be referred to as a “hand-off” from oneslip bowl 154, 158 to another and may involve additional movements ofone or more of the traveling heads 156, 160 for the second slip bowl 158to fully engage the work string 152 and for the first slip bowl 154 tofully disengage from the work string 152. The third and fourth hydraulicactuators 110-c, d may then be commanded to move the work string 152 inthe positive Z direction, while the first and second hydraulic actuators110-a, b are commanded to move in the negative Z direction. At about thelimits of travel, the hydraulic actuators 110 may be commanded to stop,bringing the work string 152, both slip bowls 154, 158, and bothtraveling heads 156, 160 to a stop with zero velocity. A hand-off isthen performed transferring the work string 152 from the grip of thesecond slip bowl 158 to the grip of the first slip bowl 154. This cyclemay be repeated, moving the work string 152 further into the well orreversed and repeated, moving the work string 152 out of the well. Insome contexts, this mode of operation may be referred to as a high speedsequential mode.

Using the high speed sequential mode, the four hydraulic actuators110-a, b, c, d may cooperate to maintain a sequence of start-stopmovements of the work string 152, driving the work string 152 at anaverage commanded velocity V to a commanded depth Z. In this mode, thetwo pairs of hydraulic actuators—hydraulic actuators 110-a, b andhydraulic actuators 110-c, d—can operate out-of-phase, handing offbetween each other, thereby achieving higher velocities of the workstring 152 than may be possible with a single pair of hydraulicactuators, for example 110-a, b. In some contexts herein, the commandedvelocity V and commanded depth Z may be referred to as a trajectory ofthe work string 152. Alternatively, a plurality of commanded velocitiesV and commanded depths Z may be concatenated into a series that may alsobe referred to as a trajectory of the work string 152.

In another case, for example when the work string 152 may be too heavyfor manipulation by one pair of hydraulic actuators 110 at a time, thefour actuators 110-a, b, c, d and the two slip bowls 154, 158 may becommanded to share the load of manipulating the work string 152. In thiscase, the first and second slip bowls 154, 158 may be engaged to gripthe work string 152 and the four hydraulic actuators 110-a, b, c, d maybe commanded to move the work string 152 in the positive Z direction toabout one limit of their travel. The four hydraulic actuators 110-a, b,c, d then may be commanded to bring the work string 152 to a stop, zerovelocity V, whereupon the stationary slip bowl 162 may be engaged togrip and hold the weight of the work string 152. When the stationaryslip bowl 162 is supporting the work string 152, the first and secondslip bowls 154, 158 may be disengaged, and the four hydraulic actuators110-a, b, c, d may be commanded to move in the negative Z direction toabout the opposite limit of their travel. The four hydraulic actuators110-a, b, c, d may then be commanded to come to a stop, zero velocity V,whereupon the first and second slip bowls 154, 158 may be commanded toengage and grip the work string 152. The stationary slip bowl 162 thenmay be commanded to disengage, and the cycle may be repeated. In somecontexts, this mode of operation may be referred to as a distributedload or high capacity sequential mode. This mode may be characterized bya coordinated sequence of start and stop operations between the twopairs of hydraulic actuators—hydraulic actuators 110-a, b and hydraulicactuators 110-c, d—working in unison and using the stationary slip bowl162 to bear the work string 152 during stops. This mode may provide acapacity to manipulate higher loads, for example a heavier work string152, but with lower velocity than may be possible with the high speedsequential mode.

In another case, for example when the weight of the work string 152 iswithin the handling capacity of one pair of hydraulic actuators 110, forexample the hydraulic actuators 110-a, b, the four hydraulic actuators110-a, b, c, d and the two slip bowls 154, 158 may be synchronized tomaintain a substantially continuous movement of the work string 152. Inother words, the hydraulic actuators 110-a, b, c, d and the slip bowls154, 158 may move in such a way as to provide substantially constantvelocity of the work string 152 or substantially constant accelerationor deceleration of the work string 152. The hand off of the work string152 between the hydraulic actuators 110-a, b, c, d and the slip bowls154, 158 may be coordinated “on the fly” to promote this continuousmotion. In some contexts, this mode of operation may be referred to as ahigh speed continuous mode. This mode may have the advantage of reducingthe power and/or energy consumption requirements necessary to start andstop the work string 152 with each motion as described in the high speedsequential mode. Additionally, this mode may reduce stress and strain onthe various components of the dual-jacking system 150 and/or thehydraulic components, thereby possibly extending the service life of thesame.

In another case, for example when the weight of the work string 152 iswithin the handling capacity of one pair of hydraulic actuators 110, forexample the hydraulic actuators 110-a, b, constraints other than themaximum handling capacity of the pairs of hydraulic actuators 110 mayconstrain the work string 152 velocities and/or accelerations. Forexample, mechanical, electrical, and/or safety constraints may limit thespeed at which a hand-off “on the fly” can be accomplished. This maximumhand-off speed may be slower than the desired or commanded velocity ofthe work string 152. In order to achieve an overall “average” workstring speed which matches the commanded velocity of the work string152, the four hydraulic actuators 110-a, b, c, d and the two slip bowls154, 158 may be synchronized. When synchronized, the four hydraulicactuators 110-a, b, c, d and the two slip bowls 154, 158 may deceleratethe work string 152 to the maximum hand-off speed during hand-offs andaccelerate the work string 152 to a velocity between hand-offs such thatthe overall average velocity of the work string 152 is the commandedvelocity of the work string 152. In some contexts, this mode ofoperation may be referred to as a high speed constrained mode.

In another case, for example when the weight of the work string 152 iswithin the handling capacity of one pair of hydraulic actuators 110, forexample the hydraulic actuators 110-a, b, mechanical, electrical, orsafety constraints or considerations may make it desirable to use thestationary slip bowl 162 during the hand off between the hydraulicactuators 110, for example between the hydraulic actuators 110-a, b andthe hydraulic actuators 110-c, d. The four hydraulic actuators 110-a, b,c, d and the three slip bowls 154, 158, and 162 may be synchronized suchthat after a stroke of manipulating the work string 152 is completed bythe hydraulic actuators 110-a, b the first slip bowl 154 hands off thework string 152 to the stationary slip bowl 162. At this point, the slipbowls 154 and 158 are both disengaged from the work string 152. Thestationary slip bowl 162 then hands off the work string 152 to thesecond slip bowl 158 with the hydraulic actuators 110-c, d in positionfor a full stroke of manipulating the work string 152. The hydraulicactuators 110-c, d then manipulate the work string 152 while thehydraulic actuators 110-a, b reposition the first slip bowl 154 to astarting position for the next hand off. In some contexts, this mode ofoperation may be referred to as a high speed sequential mode with thestationary slip. Generalizing, this mode of operation may be referred toas a three manipulator high speed sequential mode as opposed to the twomanipulator high speed sequential mode described above.

In another case, for example when the weight of the work string 152exceeds the handling capacity of one pair of hydraulic actuators 110,for example the hydraulic actuators 110-a, b, three or more pairs ofhydraulic actuators 110 may be employed to provide a high capacitycontinuous mode of operation. For example, hydraulic actuators 110-a, b,c, d, e, f may be operated with hydraulic actuators 110-a, b forming inpart a first manipulator, hydraulic actuators 110-c, d forming in part asecond manipulator, and hydraulic actuators 110-e, f forming in part athird manipulator. The first, second, and third manipulators may becoupled to slip bowls by a traveling head as depicted in FIG. 3. Thefirst and second manipulator may grip the work string 152 and move thework string while the third manipulator is repositioned. The thirdmanipulator may then grip the work string 152, and the secondmanipulator may release the work string 152. The first and thirdmanipulators may move the work string 152 while the second manipulatoris repositioned. The second manipulator may then grip the work string152, and the first manipulator may release the work string 152. Thesecond and third manipulators may move the work string 152 while thefirst manipulator is repositioned. The first manipulator may then gripthe work string 152, and the third manipulator may release the workstring 152. The cycle may be repeated to provide substantiallycontinuous movement of the work string 152. It will be appreciated byone skilled in the art that other numbers of manipulators may becombined in a fashion similar to that described above to providesubstantially continuous motions while distributing the weight of thework string 152 over multiple manipulators.

The mode of operation chosen determines how the commanded trajectoriesof the manipulators (traveling head position, traveling head velocity,slip bowl position) are computed through kinematics. Additionally, allof these modes are relevant with any number, type, or combination ofmanipulators. For example, a system which consists of four manipulatorscould be used where the weight of the work string 152 exceeds thecapacity of a single manipulator but does not exceed the capacity of twomanipulators working in unison. A mode can be envisioned where themanipulators are paired into two sets for capacity reasons and thepaired sets of manipulators are operated in a high speed continuous modeto maximize pipe speed.

Another example would be the same four manipulator system where theweight of the work string 152 exceeds the capacity of two manipulatorsbut does not exceed the capacity of three manipulators working inunison. A mode can be envisioned where there are always threemanipulators in contact with the work string 152 for capacity reasonsand the manipulators are operated in a version of the high speedcontinuous mode to maximize the velocity of the work string 152.

With multiple manipulators in a particular system a series of modes canbe envisioned where the control system automatically changes from modeto mode to optimize performance and prevent failure as the weight of thework string 152 increases or decreases.

In combination with the present disclosure, one skilled in the art mayrecombine or extend the scenarios described above to describe othercontrolling regimes, all of which are contemplated by the presentdisclosure and system.

Turning now to FIG. 4, a work string control system 200 is described.The work string control system 200 is one embodiment of the controlsystem architecture 8 described with reference to FIG. 1 above. The workstring control system 200 comprises a controller 202, a commandedtrajectory input 204, a first flow rate command 210, a first flowdirection command 212, a first slip bowl position command 214, a secondflow rate command 216, a second flow direction command 218, a secondslip bowl position command 220, a third flow rate command 222, a thirdflow direction command 224, a third slip bowl position command 226, afirst feedback vector 230, a second feedback vector 234, and a thirdfeedback vector 238. In an embodiment, any number of flow rate commandsand flow direction commands may be provided by the controller 202.Similarly, in an embodiment, any number of feedback vectors may bereceived by the controller 202. The controller 202 is configured toautomatically generate the flow rate commands 210, 216, and 222; theflow direction commands 212, 218, and 224; and the slip bowl positioncommands 214, 220, and 226 based on the commanded trajectory input 204and the feedback vectors 230, 234, and 238. In an embodiment, each oneof the commands may depend upon all of the input vectors. For example,the first flow rate command 210 may depend not only on the firstfeedback vector 230 but also on the second feedback vector 234, becausethe motions of the first and second traveling heads 154, 158 may not becommanded entirely independently of each other. In an embodiment, thethird slip bowl position command 226 may control the stationary slipbowl 162 and the third flow rate command 222 and the third flowdirection command 224 may remain zero.

In an embodiment, the controller 202 is implemented on a general purposecomputer system using digital control methods based on discrete timeprocessing of sampled inputs. In another embodiment, however, thecontroller 202 may be implemented as a combination of the generalpurpose computer system and some analog processing components and atleast part of the controller 202 may use analog control methods based oncontinuous time processing of analog inputs. Analog feedback controlsystem components are well known to those skilled in the art and may beimplemented, for example, using differential amplifiers, capacitors, andresistors to compose integrators, differentiators, amplifiers, and othercommon analog feedback control system components. General purposecomputer systems are discussed in further detail hereinafter. It will beunderstood by one skilled in the art that the several components of thecontrol system architecture 8 including the manipulator controllers20-a, b, c, the drive modulators 40-a, b, c, the manipulator observersystem 30, and the drive observer system 50 may be conceptuallyaggregated as the controller 202 and implemented in one or morecoordinated computer programs or software components that are executedon one or more computer systems.

In an embodiment, the controller 202 is coupled to the dual-jackingsystem 150 described above and is operable to control the actuators110-a, b, c, d and to control the first and second slip bowls 154, 158to manipulate the work string 152 to achieve the commanded trajectoryinput 204. In this embodiment, the first flow rate command 210 may becoupled to a first hydraulic pump 102-a (not shown) associated with thefirst and second hydraulic actuators 110-a, b, the first flow directioncommand 212 may be coupled to a first directional flow valve 104-a (notshown) associated with the first and second hydraulic actuators 110-a,b, and the first slip bowl position command 214 may be coupled to thefirst slip bowl 154. In this embodiment, the second flow rate command216 may be coupled to a second hydraulic pump 102-b (not shown)associated with the third and fourth hydraulic actuators 110-c, d, thesecond flow direction command 218 may be coupled to a second directionalflow valve 104-b (not shown) associated with the third and fourthhydraulic actuators 110-c, d, the second slip bowl position command 220may be coupled to the second slip bowl 158, and the third slip bowlposition command 226 may be coupled to the stationary slip bowl 162.

In this embodiment, velocity and position sensors coupled to one or bothof the first and second hydraulic actuator 110-a, b and pressure andflow sensors coupled to a first rod side hydraulic line 112-a (notshown) and a first piston side hydraulic line 114-a (not shown)connected in parallel to the first and second hydraulic actuators 110-a,b may be coupled to the controller 202 as the first feedback vector 230.In this embodiment, velocity and position sensors coupled to one or bothof the third and fourth hydraulic actuators 110-c, d and pressure andflow sensors coupled to a second rod side hydraulic line 112-b (notshown) and a second piston side hydraulic line 114-b (not shown)connected in parallel to the third and fourth hydraulic actuators 110-c,d may be coupled to the controller 202 as the second feedback vector234. In an embodiment, the velocity and position sensors may be coupledto the rod 116 of the hydraulic actuator 110.

Turning now to FIG. 5, an exemplary feedback vector 250 is described.The feedback vector 250 may comprise a piston side pressure feedback252, a rod side pressure feedback 254, a flow rate feedback 256, atraveling head velocity feedback 258, a traveling head position feedback260, a slip bowl position feedback 261, and a work string collarlocation feedback 262. In other embodiments, some of the depictedfeedbacks may not be present and other feedbacks not depicted may bepresent in the feedback vector 250. In another embodiment, velocity ofthe work string 152 and position of the work string 152 may be presentin the feedback vector 250.

Turning now to FIG. 6, a manipulator control system 300 is described.The manipulator control system 300 is one embodiment of portions of thecontrol system architecture 8. In the following descriptions somecontrol components associated with specific embodiments are associatedwith their corresponding generic component in the control systemarchitecture 8 depicted in FIG. 1, for example by enclosing one or morecomponents in a dotted line box and referring to the dotted line boxwith a label from the control system architecture 8 depicted in FIG. 1.The control system architecture 8 depicted in FIG. 1 should not belimited by the following description, because the specific embodimentsof control system components described hereinafter are only some of thewide variety of possible embodiments of the control system architecture8 that are contemplated by the present disclosure.

The manipulator control system 300 automatically controls a physicalsystem, for example the manipulator physical system 60, through amanipulator physical system interface 302. In an embodiment, thephysical system associated with the manipulator physical systeminterface 302 may be substantially similar to portions of thedual-jacking system 150 and portions of the two actuator hydraulicsystem 130. In another embodiment, however, the manipulator controlsystem 300 may control a different manipulator physical system 60. Themanipulator control system 300 may be said to have two degrees offreedom because it controls the first slip bowl 154 and it controls thefirst traveling head 156, for example by controlling the firstdirectional valve 104-a and the first hydraulic pump 102-a. In anembodiment, the manipulator physical system interface 302 comprises thefirst slip bowl 154, the first directional flow valve 104-a, the firsthydraulic pump 102-a, a flow sensor 310, a first pressure sensor 312-a,a second pressure sensor 312-b, a traveling head position sensor 314,and a traveling head velocity sensor 316. The manipulator control system300 may be implemented on a general purpose computer system usingdigital control methods based on discrete time processing of sampledinputs. In another embodiment, however, the control system 300 mayinclude some analog components which process continuous time inputsaccording to analog feedback control methods.

In an embodiment, the manipulator control system 300 comprises a flowregulator 320, a force modulator 322, a pressure estimator 324, atraveling head controller 326, and a traveling head position andvelocity observer 328. In other embodiments, the manipulator controlsystem 300 may comprise other components. For example, in an embodiment,the manipulator control system 300 may not comprise the pressureestimator 324, and instead the outputs of the pressure sensors 312-a, bmay be directly input to the force modulator 322. In an embodiment, themanipulator control system 300 may not comprise the traveling headposition and velocity observer 328, and instead the output of thetraveling head position sensor 314 and the output of the traveling headvelocity sensor 316 may be directly input to the traveling headcontroller 326. The flow regulator 320 in combination with the forcemodulator 322 form an embodiment of the drive modulator 40 depicted inFIG. 1. The pressure estimator 324 is an embodiment of the driveobserver system 50 depicted in FIG. 1. The traveling head position andvelocity observer 328 is an embodiment of the manipulator observersystem 30 depicted in FIG. 1. The traveling head controller 326 is anembodiment of the manipulator controller 20 depicted in FIG. 1.

In an embodiment, a slip bowl command (S_(SB)*) commands the first slipbowl 154 to an open or a closed position or state. In a differentembodiment, however, a slip bowl controller (not shown) may be employedto generate a slip bowl command based on a sensed or estimated positionof the first slip bowl 154 and based on a desired position of the firstslip bowl 154.

In an embodiment, the flow regulator 320 receives a flow rate command(Q*) input from the force modulator 322 and a flow rate feedback (Q)from the flow sensor 310 and automatically produces a current command(I*) to regulate the first hydraulic pump 102-a to provide the desiredhydraulic flow rate to the manipulator, for example to the hydraulicactuators 110-a, b. In another embodiment, however, no flow ratefeedback is provided to the flow regulator 320 which operates in anopen-loop control mode. An embodiment of the flow regulator 320 isdescribed further hereinafter.

In an embodiment, the force modulator 322 receives a traveling headforce command (F*_(TH)) and a traveling head velocity command (V*_(TH))from the traveling head controller 326. In an embodiment, the forcemodulator 322 also receives an estimated piston side pressure feedback(P̂_(RS)), an estimated rod side pressure feedback (P̂_(RS)), and anestimated flow rate disturbance feedback (Q̂_(D)) from the pressureestimator 324. In combination with the present disclosure, one skilledin the art will readily appreciate that an estimated parameter value,while it is related to a sensed parameter value, may be different fromthe sensed parameter value. For example, an estimated parameter valuemay be a smoothed or filtered version of the sensed parameter value thatattenuates noise produced by a sensor or by an environment.Additionally, an estimated parameter value may partially reduce orremove phase shifts and/or time lags of system response. In anotherembodiment, however, the force modulator 322 receives a sensed pistonside pressure feedback (P_(PS)) and a sensed rod side pressure feedback(P_(RS)), for example in an embodiment which does not comprise thepressure estimator 324. The force modulator 322 automatically producesthe flow rate command Q* and provides the flow rate command Q* to theflow regulator 320. The force modulator 322 also automatically producesa directional flow valve command (S_(DV)*) to control the state of thedirectional flow valve 104. In an embodiment that comprises a pressureestimator 324, the force modulator 322 also automatically produces anobserver feed forward flow rate command Q*_(O) and provides the observerfeed forward flow rate command Q*_(O) to the pressure estimator 324. Inan embodiment, the directional flow valve command may be mapped by adigital-to-analog converter device (not shown) to produce an electricalcurrent to energize the first or the second solenoid to actuate thediverting spool to control the first directional flow valve 104-a. Anembodiment of the force modulator 322 is described further hereinafter.

In an embodiment, the pressure estimator 324 receives a sensed pistonside pressure (P_(PS)) input, a sensed rod side pressure (P_(RS)) input,the directional flow valve command (S_(DV)*) input, the observer feedforward flow rate command (Q*_(O)) input, an estimated traveling headposition (Ẑ_(TH)) input, an estimated traveling head velocity (V̂_(TH))input and automatically produces the estimated piston side pressure, theestimated rod side pressure, and the estimated disturbance flow rate. Inanother embodiment, one or more of the estimated traveling head position(Ẑ_(TH)) and the estimated traveling head velocity (V̂_(TH)) may besensed rather than estimated values. Each of the estimated pressures area zero time lagged, filtered signal. An embodiment of the pressureestimator 324 is discussed further hereinafter.

In an embodiment, the traveling head controller 326 receives a travelinghead command input vector 340 that comprises a traveling head positioncommand (Z_(TH)*), the traveling head velocity command (V_(TH)*), atraveling head acceleration command (A_(TH)*), and a feed forward workstring load on the traveling head (F*_(WS/TH)). The traveling headcontroller 326 also receives an estimated traveling head position(Ẑ_(TH)) input, an estimated traveling head velocity (V̂_(TH)) input andan estimated traveling head force disturbance (F̂_(D)) input from theposition and velocity observer 328. In an embodiment, however, themanipulator control system 300 does not comprise a traveling headposition and velocity observer 328, and the traveling head controller326 receives a sensed traveling head position (Z_(TH)) from thetraveling head position sensor 314 and/or a sensed traveling headvelocity (V_(TH)) from the traveling head velocity sensor 316. Ingeneral, a velocity sensor may provide a more accurate indication ofmanipulator velocity, for example traveling head velocity, thandifferentiating the output of a manipulator position sensor over time tocalculate manipulator velocity, because the differentiation operationmay produce unreliable results caused by noise in the signal generatedby the position sensor 314. The traveling head controller 326automatically produces the traveling head force command F*_(TH) andprovides the traveling head force command F*_(TH) to the force modulator322. The traveling head controller 326 automatically produces theobserver feed forward traveling head force command F*_(THO) and providesthe observer feed forward traveling head force command F*_(THO) to thetraveling head position and velocity observer 328. An embodiment of thetraveling head controller 326 is discussed further hereinafter.

The traveling head position and velocity observer 328 receives theobserver feed forward traveling head force command F*_(THO) from thetraveling head controller 326, the sensed traveling head position inputfrom the traveling head position sensor 314, and the sensed travelinghead velocity input from the traveling head velocity sensor 316. Thetraveling head position and velocity observer 328 automatically producesthe estimated traveling head position, the estimated traveling headvelocity, and the estimated traveling head force disturbance andprovides the estimated traveling head position, the estimated travelinghead velocity, and the estimated traveling head force disturbance to thetraveling head controller 326. Each of the estimated traveling headposition and estimated traveling head velocity is a zero time lagged,filtered signal. An embodiment of the traveling head position andvelocity observer 328 is discussed further hereinafter. In combinationwith the present disclosure, one skilled in the art will readilyappreciate that an estimated parameter value, while it is related to asensed parameter value, may be different from the sensed parametervalue. For example, an estimated parameter value may be a smoothed orfiltered version of the sensed parameter value that attenuates noiseproduced by a sensor or by an environment. Additionally, an estimatedparameter value may partially reduce or remove phase shifts and/or timelags of system response.

Turning now to FIG. 7, an embodiment of the flow regulator 320 and anembodiment of the hydraulic pump 102 are discussed. The flow regulator320, in combination with the force modulator 322 discussed below,comprise an embodiment of the drive modulator 40 of the control systemarchitecture 8 described with reference to FIG. 1. The flow regulator320 comprises a plurality of functional blocks including summationjunctions, integrators, and gain units. The flow regulator 320 comprisesa proportional-integral (PI) controller portion, a command feed-forwardportion, and a pump control gain portion. The general purpose of the PIcontroller portion is to correct the error between a sensed flow rateand a flow rate command by producing a corrective signal that tends todrive the sensed flow rate to the flow rate command. The general purposeof the command feed-forward portion is to provide a command feed-forwardsignal that comprises a substantial component of the drive signal tocontrol a motor that drives the hydraulic pump 102 based on the flowrate command, which may promote the PI controller portion being moresuitably tuned to the purpose of correcting for dynamic transients anddisturbances, such as changes of the physical system, sensors, orerrors. Generally, in control systems analysis, disturbance termscorrespond to imperfections or errors, for example extraordinaryconditions, imperfect measurements or sensing of system parameters,irregularities such as bubbles in the hydraulic fluid, etc.

A sensed flow rate 406 is negatively summed with a flow rate command 402by a first summation junction 408 to determine a flow rate error term.The sensed flow rate 406 provides a negative feedback term. The outputof the first summation junction 408 is amplified by a first proportionalgain 410. The output of the first summation junction 408 is integratedby a first integrator 412 and then amplified by a first integral gain414. The output of the first proportional gain 410 and the output of thefirst integral gain 414 are summed by a second summation junction 416.The components 408, 410, 412, 414, and 416 comprise a PI controllerportion. The output of the second summation junction 416 may be viewedas a corrective signal that tends to drive the sensed flow rate 406 tothe value of the flow rate command 402. In an embodiment, the positionof the first integrator 412 and the first integral gain 414 may bereversed, and the flow rate error term, the output of the firstsummation junction 408, may be first amplified by the first integralgain 414 and then may be integrated by the first integrator 412. Incombination with the present disclosure, the values of the firstintegral gain 414 and of the first proportional gain 410 may be readilydetermined by one skilled in the control systems art. The process ofdetermining proportional, integral, and derivative gains in controlsystems is discussed in further detail hereinafter.

The command feed-forward signal is produced by amplifying the flow ratecommand 402 by a first feed-forward gain 418. The first feed-forwardgain 418 is inversely proportional to an estimate of the angularvelocity or rate of rotation of the motor driving the hydraulic pump102. In an embodiment, the first feed-forward gain 418 may be a constantvalue, for example a constant value proportional to the reciprocal ofthe designed steady-state angular velocity of the motor. In anotherembodiment, however, the first feed-forward gain 418 may be determinedbased on the actual value of the angular velocity ω_(P) of the motor,for example the value of motor angular velocity determined by a sensor.The command feed-forward signal is summed with the output of the secondsummation junction 416 by the third summation junction 420. The outputof the third summation junction 420 is amplified by a pump control gain422 to produce a current command 404. In combination with the presentdisclosure, the pump control gain 422 may be readily determined by oneskilled in the control systems art based on design data provided by themanufacturer of the hydraulic pump 102. In an embodiment, the pumpcontrol gain 422 may not remain constant and may vary with the value ofthe output of the third summation junction 420. In this case the flowregulator may determine the pump control gain 422 using a look-up table,gain scheduling, or other function definition. In some contexts, thefirst feed-forward gain 418 and the pump control gain may be referred toas a model or a portion of a model of the flow regulator 320 or of thedrive modulator 40.

In an embodiment, the hydraulic pump 102 is an axial piston pump system308 comprising a motor that turns a swash plate that drives an axialpiston pump. The axial piston pump system 308 may comprise a currentregulator 430, a pump swash plate actuator 432, a pump rotationmultiplication junction 434, a pump chamber 436, and a flow sensor 310.The current regulator 430 outputs a control current to actuate an angleof displacement of the pump swash plate actuator 432 based on thecurrent command 404 provided by the flow regulator 320. The angle ofdisplacement of the pump swash plate actuator 432 determines the amountof piston displacement as the pistons reciprocate within the pumpchamber 436.

The swash plate actuator 432 is illustrated as coupled to the pumpchamber 436 through the pump rotation multiplication junction 434illustrated as having a rotational input designated by ω_(p). The pistondisplacement, in combination with the rate of rotation of the pump swashplate, determines the flow output of the hydraulic pump 102. The outputsof the pump chamber 436 include the pump pressure output 440 and thepump flow output 442. The inputs of the pump chamber 436 include a pumpback pressure 444, and a pump inlet pressure P_(S). The flow sensor 310provides the sensed flow rate 406.

In an embodiment, the value of the first proportional gain 410 and thevalue of the first integral gain 414 are both set to zero, the output ofthe second summation junction 416 is substantially zero, and the outputof the third summation junction is substantially determined by theoutput of the first feed-forward gain 418. In another embodiment, thecomponents 408, 410, 412, 414, and 416—the PI controller portion—are notpart of the flow regulator 320. In both these embodiments the sensedflow rate 406 is not used to generate the current command 404. These twoembodiments may be employed when there is no flow sensor 310 available,when the sensed flow rate 406 output by the flow sensor 310 isunreliable or time lags the actual flow rate excessively, or when thepump swash plate actuator 432 has a low frequency response.

Turning now to FIG. 8, an embodiment of the force modulator 322 isdiscussed. The force modulator 322, in combination with the flowregulator 320 discussed above, comprise an embodiment of the drivemodulator 40 of the control system architecture 8 described withreference to FIG. 1. The combination of the force modulator 322 and theflow regulator 320 may be said to transform or map a manipulator forcecommand and a manipulator velocity command to an actuator controlsignal. The force modulator 322 comprises a proportional controllerportion, a command feed-forward portion, and a directional valvemodulator 514. The general purpose of the proportional gain controlleris to correct the error between a traveling head force command 504 and acalculated or estimated force by producing a corrective signal thattends to drive the estimated force to the value of the traveling headforce command 504. The calculated force is determined based on sensed orestimated pressures in the rod side pressure line 112 and in the pistonside pressure line 114. In an embodiment, it is assumed that thepressure sensed in the rod side pressure line 112 is substantially thesame as the pressure in the rod side chamber 120 and that the pressuresensed in the piston side pressure line 114 is substantially the same asthe pressure in the piston side chamber 122. In another embodiment,however, pressure sensors may be placed in the rod side chamber 120 andin the piston chamber 122. The estimated force is negatively summed withthe traveling head force command 504 by a fourth summation junction 506to produce a force error term. The estimated force provides a negativefeedback term. The output of the fourth summation junction 506 isamplified by a second proportional gain 508. The components 506 and 508comprise a proportional controller. In combination with the presentdisclosure, the value of the second proportional gain 508 may be readilydetermined by one skilled in the control systems art.

The command feed-forward portion produces a command feed-forward signalby amplifying a traveling head velocity command 502 by a directionalarea gain 510. Amplifying the traveling head velocity command 502 by anarea term generates a volumetric rate of change term, or a flow rateterm, corresponding to the flow rate of hydraulic fluid that promotesdriving the traveling head velocity to achieve the value of thetraveling head velocity command 502. In an embodiment, the directionalarea gain 510 may be determined based on the effective surface area ofthe piston 118 of the hydraulic actuator 110. In another embodiment,because the effective surface area of the piston 118 is greater in thepiston side chamber 122 than in the rod side chamber 120, a differentvalue of the directional gain 510 may be used depending upon thepolarity or sense of direction of the velocity command 502. As notedabove with respect to FIG. 2A, the effective surface area of the pistonin the rod side chamber 122 is decreased by the cross-sectional area ofthe rod 116. In another embodiment, a single value of directional gain510 may be used that is based on an average of the effective surfacearea of the piston in the piston side chamber 122 and the effectivesurface area of the piston in the rod side chamber 120. In the dualjacking system 150 embodiment, because two actuators 110-a, b areemployed to manipulate the work string 152, the area gains of interestmay be determined based on twice the effective surface area of thepiston in the piston side chamber 122 side and twice the effectivesurface area of the piston in the rod side chamber 120. The output ofthe second proportional gain 508 is summed with the output of thedirectional gain 510 by a fifth summation junction 512. In the eventthat additional hydraulic actuators 110 are employed together, thedirectional gain 510 may be determined based on multiplying theeffective surface area of the piston in the piston side chamber 122 andthe effective surface area of the piston in the rod side chamber 120 bythe number of hydraulic actuators 110. In another embodiment, however,the directional gain 510 may be determined in another way.

The force modulator 322 also comprises the directional valve modulator514. The directional valve modulator 514 determines a directional flowvalve command 530 based on the output of the fifth summation junction512. The directional flow valve command 530 may control the directionalflow valve 104 to direct the fluid flow to the rod side chamber 120, tothe piston side chamber 122, or to the hydraulic return line 108. In anembodiment, the directional flow valve command 530 may be mapped by adigital-to-analog converter device (not shown) to produce an electricalcurrent to energize the first or the second solenoid to actuate thediverting spool to control the directional flow valve 104. In anembodiment, the directional valve modulator 514 outputs an observer feedforward flow rate command 403. In an embodiment, the directional valvemodulator 514 also outputs a flow command that is summed with anestimate of the hydraulic fluid flow disturbance 650 to produce the flowrate command 402. The hydraulic fluid flow disturbance 650 is discussedfurther below with reference to FIG. 10. The estimate of the hydraulicfluid flow disturbance 650 may take account of fluid leakage past sealswithin the directional flow valve 104 and/or other hydraulic seals inthe hydraulic system. In another embodiment, however, the directionalvalue modulator 514 directly outputs the flow rate command 402 and nohydraulic fluid flow disturbance term is considered.

The force modulator 322 also comprises a portion for calculating anestimated manipulator force as the force produced by the piston sidechamber 122 subtracted from the force produced by the rod side chamber120. The estimated piston side pressure 532 is amplified by a pistonside area gain 546 to determine the force produced by the piston sidechamber 122 of the hydraulic actuators 110-a,b. The estimated rod sidepressure 534 is amplified by a rod side area gain 554 to determine theforce produced by the rod side chamber 120 of the hydraulic actuators110-a, b. Because in the subject embodiment two actuators 110-a, b areemployed, the area gains 546, 554 are represented as multiplying theirrespective areas by a factor of two. In some contexts, the area gains546, 554 may be referred to as a model or a model portion of the forcemodulator 322 or of the drive modulator 40. A seventh summation junction556 sums the negative value of the piston side force with the positivevalue of the rod side force to determine the estimated traveling headforce F̂_(TH). In another embodiment, other control structures may beemployed to estimate force. In another embodiment, sensed values of rodside pressure and piston side pressure may be used instead of theestimated rod side pressure 534 and the estimated piston side pressure532, respectively.

Turning now to FIG. 9, an embodiment of the traveling head controller326 is described. The traveling head controller 326 is one embodiment ofthe manipulator controller 20 of the control system architecture 8described above with reference to FIG. 1. The traveling head controller326 comprises a proportional-integral-derivative (PID) controllerportion and a command feed-forward portion. The traveling headcontroller 326 also comprises constants to compensate or offset theweight and the damping gain of the traveling head 156, 160.

An estimated traveling head position 610 is negatively summed with atraveling head position command 602 by an eighth summation junction 608to determine a traveling head position error term. The estimatedtraveling head position 610 provides a negative feedback term. Theoutput of the eighth summation junction 608 is amplified by a thirdproportional gain 616. The output of the eighth summation junction 608is integrated by a second integrator 618 and amplified by a secondintegral gain 620. In another embodiment, the output of the eighthsummation junction 608 is first amplified by the second integral gain620 and then integrated by the second integrator 618. An estimatedtraveling head velocity 606 is negatively summed with the traveling headvelocity command 502 by a ninth summation junction 612 to determine atraveling head velocity error term. The estimated traveling headvelocity 606 provides a negative feedback term. The output of the ninthsummation junction 612 is amplified by a first derivative gain 622. Theprocessing of the traveling head velocity error term is considered to bea derivative component with respect to traveling head position becausegenerally velocity is the derivative of position. In another embodiment,the sensed traveling head position and sensed traveling head velocityare used in place of the estimated traveling head position 610 and theestimated traveling head velocity 606, respectively. A tenth summationjunction 624 sums the outputs of the third proportional gain 616, thesecond integral gain 620, and the first derivative gain 622. Thecomponents 608, 612, 616, 618, 620, 622, and 624 comprise a PIDcontroller portion. The output of the tenth summation junction 624 maybe viewed as a corrective signal that tends to drive the estimatedtraveling head position 610 and the estimated traveling head velocity606 to the values of the traveling head position command 602 and thetraveling head velocity command 502. In combination with the presentdisclosure, the values of the third proportional gain 616, the secondintegral gain 620, and the first derivative gain 622 may readily bedetermined by one skilled in the control systems art.

A traveling head acceleration command 634 is amplified by a secondfeed-forward gain 636 to produce a feed-forward signal. The secondfeed-forward gain 636 is proportional to the estimated mass of thetraveling head. The feed-forward term corresponds to a force term,because the product of an acceleration multiplied by a mass isequivalent to a force. The estimated traveling head velocity 606 isamplified by an estimated traveling head damping gain 640. The output ofthe tenth summation junction 624 is summed with the output from thesecond feed-forward gain 636, the output from the damping gain 640, andthe negative of the estimated traveling head weight 638 by an eleventhsummation junction 641 to produce an observer feed forward travelinghead force command 643. The output of the eleventh summation junction641 is summed with negative values of a feed forward work string loadcommand 632 corresponding to the predicted weight of the work string 152on the traveling head 156, 160 and an estimated traveling headdisturbance force term 644 by a twelfth summation junction 642 toproduce the traveling head force command 504. In some contexts, thetraveling head force command 504 may be referred to more generally as amanipulator force command. In another embodiment, the estimatedtraveling head disturbance force term 644 is not available and hence isnot summed by the twelfth summation junction 642. In combination withthe present disclosure, one skilled in the art may readily determine thesecond feed-forward gain 636 and the traveling head damping gain 640 byexperimentally collecting data, for example velocity, position,acceleration, and/or pressure data, and fitting these gain values tothis data, a technique which may be commonly performed by one skilled inthe control systems art. In some contexts, the second feed-forward gain636 and the estimated traveling head damping gain 640 may be referred toas a model of the traveling head and/or the manipulator.

Turning now to FIG. 10, a block diagram of the pressure estimator 324 isdescribed. The pressure estimator 324 is one embodiment of the driveobserver 50 of the control system architecture 8 described withreference to FIG. 1. The pressure estimator 324 comprises a directionalvalve command feed forward component 646, a rod side pressure observer647, a piston side pressure observer 648, and a directional valvedisturbance flow component 649. The pressure estimator 324 receivesinputs from the directional flow valve command 530, the observer feedforward flow rate command 403, the sensed rod side pressure 652, thesensed piston side pressure 676, the estimated traveling head position610, and the estimated traveling head velocity 606. In anotherembodiment, sensed values for traveling head position and traveling headvelocity are used in place of the estimated traveling head position 610and the estimated traveling head velocity 606, respectively. Thepressure estimator 324 outputs the flow disturbance 650, the estimatedpiston side pressure 532, and the estimated rod side pressure 534.

The directional valve command feed forward component 646 receives thedirectional flow valve command 530 and the observer feed forward flowrate command 403 as inputs and outputs a rod side flow command 667 and apiston side flow command 690. When the directional flow valve command530 has a piston side value, the directional flow valve 104 is selectedto direct hydraulic fluid under pressure from the hydraulic pressuresupply line 106 to the piston side hydraulic line 114 into the pistonside chamber 122 and to return hydraulic fluid from the rod side chamber120 to the rod side hydraulic line 112 to the hydraulic return line 107to the hydraulic fluid reservoir 108. When the directional flow valvecommand 530 has a piston side value, the directional valve command feedforward component 646 determines the piston side flow command 690 to beproportional to the value of the observer feed forward flow rate command403 and the rod side flow command 667 to be proportional to the negativevalue of the observer feed forward flow rate command 403 multiplied bythe constant determined as the effective surface area of the piston 118in the rod side chamber 120 divided by the effective surface area of thepiston 118 in the piston side chamber 122.

When the directional flow valve command 530 has a rod side value, thedirectional flow valve 104 is selected to direct hydraulic fluid underpressure from the hydraulic pressure supply line 106 to the rod sidehydraulic line 112 into the rod side chamber 120 and to return hydraulicfluid from the piston side chamber 122 to the piston side hydraulic line114 to the hydraulic return line 107 to the hydraulic fluid reservoir108. When the directional flow valve command 530 has a rod side value,the directional valve command feed forward component 646 determines therod side flow command 667 to be proportional to the value of theobserver feed forward flow rate command 403 and the piston side flowcommand 690 to be proportional to the negative value of the observerfeed forward flow rate command 403 multiplied by the constant determinedas the effective surface area of the piston 118 in the piston sidechamber 122 divided by the effective surface area of the piston 118 inthe rod side chamber 120. This may be expressed symbolically by:

S*_(DV)=Piston Side

Q*_(PS)αQ*_(O)

Q*_(RS)α(−Q*_(O))(A_(RS)/A_(PS))

S*_(DV)=Rod Side

Q*_(PS)α(−Q*_(O))(A_(PS)/A_(RS))

Q*_(RS)αQ*_(O)

In an embodiment, the constant of proportionality is unity, but in otherembodiments a non-unity constant of proportionality may be used. In someembodiments, when the directional flow valve command 530 has a pistonside value, the piston side flow command 690 is proportional to thevalue of the observer feed forward flow rate command 403 and the rodside flow command 667 is set to about zero; when the directional flowvalve command 530 has a rod side value, the rod side flow command 667 isproportional to the observer feed forward flow rate command 403 and thepiston side flow command 690 is set to about zero. The directional valvecommand feed forward component 646 may be implemented as a softwarecomponent, a function call, or a portion of a software program thatexecutes on a processor of a general purpose computer.

The rod side pressure observer 647 receives the sensed rod side pressure652 the rod side flow command 667, the estimated traveling head position610, and the estimated traveling head velocity 606 and outputs theestimated rod side pressure 534 and an estimated rod side flowdisturbance 645. The piston side pressure observer 648 receives thesensed piston side pressure 676 the piston side flow command 690, theestimated traveling head position 610, and the estimated traveling headvelocity 606 and outputs the estimated piston side pressure 532 and anestimated piston side flow disturbance 651. Both the rod side pressureobserver 647 and the piston side pressure observer 648 are discussed ingreater detail hereinafter.

The directional valve disturbance flow component 649 receives thedirectional flow valve command 530, the estimated rod side flowdisturbance 645, and the estimated piston side flow disturbance 651 asinputs and outputs the flow disturbance 650. When the directional flowvalve command 530 has a piston side value, the directional valvedisturbance flow component 649 sets the value of the flow disturbance650 to the value of the estimated piston side flow disturbance 651. Whenthe directional flow valve command 530 has a rod side value, thedirectional valve disturbance flow component 649 sets the value of theflow disturbance 650 to the value of the estimated rod side flowdisturbance 645. The directional valve disturbance component 649 may beimplemented as a software component, a function call, or a portion of asoftware program that executes on a processor of a general purposecomputer.

Turning now to FIG. 11, an embodiment of the rod side pressure observer647 and the piston side pressure observer 648 are discussed. Each of thepressure observers 647, 648 have a similar structure and are eachdirected to producing an estimated pressure output and an estimated flowdisturbance term output. In combination with the present disclosure, oneskilled in the art will readily appreciate that an estimated parametervalue, while it is related to a sensed parameter value, may be differentfrom the sensed parameter value. For example, an estimated parametervalue may be a smoothed or filtered version of the sensed parametervalue that attenuates noise produced by a sensor or by an environment.Additionally, an estimated parameter value may partially reduce orremove phase shifts and/or time lags of system response. Each of thepressure observers 647, 648 includes a proportional-integral (PI)controller portion, a flow feed-forward portion, and a model portion.While the discussion below is based on inputting an estimated travelinghead position Ẑ_(TH) and an estimated traveling head velocity V̂_(TH) toeach of the pressure observers 647, 648, in another embodiment a sensedtraveling head position Z_(TH) and a sensed traveling head velocityV_(TH) may be input to each pressure observer 647, 648 in the place ofthe estimated traveling head position Ẑ_(TH) and the estimated travelinghead velocity V̂_(TH).

An estimated rod side pressure 673 is negatively summed with a sensedrod side pressure 652 by a thirteenth summation junction 654 to producea rod side pressure error term. The estimated rod side pressure 673 is anegative feedback term. The sensed rod side pressure 652 may be providedby the second pressure sensor 312-b. The output of the thirteenthsummation junction 654 is amplified by a fourth proportional gain 656.The output of the thirteenth summation junction 654 is first integratedby a third integrator 658 and then amplified by a third integral gain660. In another embodiment, the output of the thirteenth summationjunction 654 may by first amplified by the third integral gain 660 andthen integrated by the third integrator 658. The outputs of the fourthproportional gain 656 and the third integral gain 660 are summed by afourteenth summation junction 662. The components 654, 656, 658, 660,and 662 comprise a PI controller portion.

In combination with the present disclosure, the values of the fourthproportional gain 656 and the third integral gain 660 may be readilydetermined by one skilled in the control systems art. In an embodiment,the values of the fourth proportional gain 656 and the third integralgain 660 are not constant but may vary based on the estimate of thetraveling head position Ẑ_(TH), which may be referred to as gainscheduling. In an embodiment, the gain schedule may be looked up in atable. In another embodiment, the gain schedule may be defined by amathematical function dependent on the estimate of the traveling headposition Ẑ_(TH). In another embodiment, the gain schedule may be definedby another method. Gain scheduling may be useful for achieving stableand fast response across the operating range of the actuators 110. Forexample, the gains may be based on the volume of the rod side chamber120 which may vary substantially over the full range of travel of thepiston 118.

The components 654, 656, 658, 660, and 662 which comprise the PIcontroller portion may be viewed as a filtering and/or smoothingmechanism to attenuate noise associated with the second pressure sensor312-b and/or the operating environment. The output of the fourteenthsummation junction 662 may be viewed as a corrective signal that tendsto drive the estimated rod side pressure 673 to the sensed rod sidepressure 652. The output of the fourteenth summation junction 662 mayalso be viewed as the estimated rod side flow disturbance 645. In somecontexts, the estimated rod side flow disturbance 645 may be referred toas an estimated flow disturbance value that is a smoothed value andbased on sensor information.

The flow feed-forward portion produces a flow rate by amplifying theestimated traveling head velocity 606 of the manipulator by a rod sidearea gain 666. This flow rate is associated with the flow of hydraulicfluid into and out of the rod side chamber 120 as the manipulator movesin the Z-axis of motion. The value of the rod side area gain 666 isproportional to the effective surface area of the rod side of thepiston, the area of the piston 118 compensated for by the area of therod 116 as described above. When two hydraulic actuators 110 areemployed, for example the first and second hydraulic actuators 110-a, b,then the area gain may be doubled. The output of the rod side area gain666 is negatively summed with the output of the fourteenth summationjunction 662 and with a rod side flow command 667 by a fifteenthsummation junction 668. The effect of the summation of the negative ofthe rod side gain 666, the rod side flow command 667, and the outputfrom the fourteenth summation junction 662 is to produce through themodel a filtered pressure related value that is zero time lagged or zerophase lagged with respect to the sensed rod side pressure 652.

The output of the fifteenth summation junction 668 is integrated by afourth integrator 672 and then amplified by a rod side model gain 670.In another embodiment, the output of the fifteenth summation junction668 may be first multiplied by the rod side model gain 670 and thenintegrated by the fourth integrator 672. The value of the rod side modelgain 670 is proportional to K̂_(oil), the estimated bulk modulus of thehydraulic fluid, and is inversely proportional to {circumflex over(∇)}_(RS), the estimated volume of the rod side chamber 120 for both thefirst and second hydraulic actuators 110-a, b and the hydraulic lines,for example the rod side hydraulic line 112 associated with the firstand second hydraulic actuators 110-a, b. Because the volume of the rodside chamber 120 varies with the estimated traveling head positionẐ_(TH), in an embodiment the value of the rod side model gain 670 mayvary and may be determined using gain scheduling in a manner similar tothat discussed above.

The estimated bulk modulus of the hydraulic fluid, K̂_(oil), is anindication of the compressibility of the hydraulic fluid. In anembodiment, the value of the estimated hydraulic bulk modulus K̂_(oil)may be about 180,000 pounds per square inch (PSI), but in otherembodiments and in using other hydraulic fluids a different estimatedbulk modulus K̂_(oil) may be used. The volume of the rod side chamber120, in an embodiment, may be calculated from an about ten foot strokeand an about seven and one half inch bore or diameter. In otherembodiments, different dimensions of the rod side chamber 120 may beappropriate. The calculation of the volume of the rod side chamber 120should take account of the volume consumed by the rod 116. Incombination with the present disclosure, the value of the rod side modelgain 670 may be readily determined by one skilled in the control systemsart.

The integration of the flow term and multiplying through by the rod sidemodel gain 670 has the effect of transforming the flow term output bythe fifteenth summation junction 668 into a pressure term. The output ofthe rod side model gain 670 is the estimated rod side pressure 673.

An estimated piston side pressure 697 is negatively summed with a sensedpiston side pressure 676 by a sixteenth summation junction 678 toproduce a piston side pressure error term. The estimated piston sidepressure 697 is a negative feedback term. The sensed piston sidepressure 676 may be provided by the first pressure sensor 312-a. Theoutput of the sixteenth summation junction 678 is amplified by a fifthproportional gain 680. The output of the sixteenth summation junction678 is integrated by a fifth integrator 682 and then amplified by afourth integral gain 684. In another embodiment, the output of thesixteenth summation junction 678 may be first amplified by the fourthintegral gain 684 and then integrated by the fifth integrator 682. Theoutputs of the fifth proportional gain 680 and the fourth integral gain684 are summed by a seventeenth summation junction 686. The components678, 680, 682, 684, and 686 comprise a proportional-integral (PI)controller portion. In combination with the present disclosure, thevalues of the fifth proportional gain 680 and the fourth integral gain584 may be readily determined by one skilled in the control systems art.In an embodiment, for the same reasons discussed above with respect tothe rod side pressure observer 647, the values of the fourthproportional gain 680 and the fourth integral gain 684 may not beconstant but may be determined by gain scheduling, by mathematicalfunction dependent on the estimate of the traveling head positionẐ_(TH), or by some other method.

The components 678, 680, 682, 684, and 686 which comprise the PIcontroller portion may be viewed as a filtering and/or smoothingmechanism to attenuate noise associated with the first pressure sensor312-a and/or the operating environment. The output of the seventeenthsummation junction 686 may be viewed as a corrective signal that tendsto drive the estimated piston side pressure 697 to the sensed pistonside pressure 676. The output of the seventeenth summation junction 686may also be viewed as an estimated piston side flow disturbance 651. Insome contexts, the estimated piston side flow disturbance 651 may bereferred to as an estimated flow disturbance value that is a smoothedvalue and based on sensor information.

The command feed-forward portion produces a flow rate by amplifying theestimated traveling head velocity 606 of the manipulator by a pistonside area gain 688. This flow is associated with the flow of hydraulicfluid into and out of the piston side chamber 122 as the manipulatormoves in the Z-axis of motion. The value of the piston side area gain688 is proportional to the area of the piston 118. When two hydraulicactuators 110 are employed, for example the first and second hydraulicactuators 110-a, b, then the piston side area gain 688 may be doubled.The output of the piston side area gain 688 is positively summed withthe output of the seventeenth summation junction 686 and with a pistonside flow command 690 by an eighteenth summation junction 692. The senseof summing of the traveling head velocity and area product is differentfor the piston pressure observer 648 versus the rod side pressureobserver 647 because the direction of traveling head motion has oppositeflow effects on the rod side chamber 120 and the piston side chamber122. The effect of the summation of the output of the piston side areagain 688, the piston side flow command 690, and the output from theseventeenth summation junction 686 is to produce through the model afiltered pressure related value that is zero time lagged or zero phaselagged with respect to the sensed piston side pressure 676.

The output of the eighteenth summation junction 692 is integrated by asixth integrator 696 and then amplified by a piston side model gain 694.In another embodiment, the output of the eighteenth summation junction692 may be first amplified by the piston side model gain 694 and thenintegrated by the sixth integrator 696. The value of the piston sidemodel gain is proportional to K̂_(oil), the estimated bulk modulus of thehydraulic fluid, and is inversely proportional to {circumflex over(∇)}_(PS), the estimated volume of the piston side chamber 122 for boththe first and second hydraulic actuators 110-a, b and the hydrauliclines, for example the piston side hydraulic line 114 associated withthe first and second hydraulic actuators 110-a, b. Because the volume ofthe piston side chamber 122 varies with the estimated traveling headposition Ẑ_(TH), in an embodiment the value of the piston side modelgain 694 may be determined using gain scheduling in a manner similar tothat discussed above.

The integration of the flow term and multiplying through by piston sidemodel gain 694 has the effect of transforming the flow term output bythe eighteenth summation junction 692 into a pressure term. The outputof the piston side model gain 694 is the estimated piston side pressure697.

In some contexts, the model portion of the rod side pressure observer647 may be considered to comprise the rod side area gain 666 and the rodside model gain 670, and these gains are based on the estimatedeffective rod side piston area, the estimated hydraulic fluid bulkmodulus, and the estimated variable rod side chamber volume. In somecontexts the model portion of the piston side pressure observer 648 maybe considered to comprise the piston side area gain 688 and the pistonside model gain 694, and these gains are based on the estimatedeffective piston side piston area, the estimated hydraulic fluid bulkmodulus, and the estimated variable piston side chamber volume. In somecontexts, the model portion of the rod side pressure observer 647 andthe model portion of the piston side pressure observer 648 may bereferred to as a model of the hydraulic actuator 110 with reference toFIG. 2A or of the hydraulic actuators 110-a, 110-b with reference toFIG. 2B.

Turning now to FIG. 12, an embodiment of the traveling head position andvelocity observer 328 is described. The traveling head position andvelocity observer 328 is one embodiment of the manipulator observer 30of the control system architecture 8 described with reference to FIG. 1.The traveling head position and velocity observer 328 may be referred toin some contexts as a manipulator position and velocity observer. Thetraveling head position and velocity observer 328 provides the estimateof traveling head position 610, the estimate of traveling head velocity606, and the estimate traveling head disturbance force term 644. Incombination with the present disclosure, one skilled in the art willreadily appreciate that an estimated parameter value, while it isrelated to a sensed parameter value, may be different from the sensedparameter value. For example, an estimated parameter value may be asmoothed or filtered version of the sensed parameter value thatattenuates noise produced by a sensor or by an environment.Additionally, an estimated parameter value may partially reduce orremove phase shifts and/or time lags of system response. The travelinghead position and velocity observer 328 comprises aproportional-integral-derivative (PID) controller portion, afeed-forward portion, and a model portion.

The estimated traveling head position 610 is negatively summed with asensed traveling head position 730 by a nineteenth summation junction734 to determine a sensed traveling head position error. The estimatedtraveling head position 610 provides a negative feedback term. Theoutput of the nineteenth summation junction 734 is amplified by a sixthproportional gain 736. The output of the nineteenth summation junction734 is integrated by a seventh integrator 738 and then amplified by afifth integral gain 740. In another embodiment, the output of thenineteenth summation junction 734 may be first amplified by the fifthintegral gain 740 and then may be integrated by the seventh integrator738. The estimated traveling head velocity 606 is negatively summed witha sensed traveling head velocity 732 by a twentieth summation junction742 to determine a sensed traveling head velocity error. The estimatedvelocity 606 provides a negative feedback term. The output of thetwentieth summation junction 742 is amplified by a second derivativegain 744. The processing of the sensed traveling head velocity errorterm is considered to be a derivative component with respect to thesensed traveling head position because generally velocity is thederivative of position. A twenty-first summation junction 746 sums theoutputs of the sixth proportional gain 736, the fifth integral gain 740,and the second derivative gain 744. The components 734, 736, 738, 740,742, 744, and 746 comprise a PID controller portion. In combination withthe present disclosure, the values of the sixth proportional gain 736,the fifth integral gain 740, and the second derivative gain 742 may bereadily determined by one skilled in the control systems art.

The components 734, 736, 738, 740, 742, 744, and 746 which comprise thePID controller portion may be viewed as a filtering and/or smoothingmechanism to attenuate noise associated with the sensed traveling headposition 730, the sensed traveling head velocity 732, and/or theoperating environment. The output of the twenty-first summation junction746 may be viewed as a corrective signal that tends to drive theestimated traveling head position 610 and estimated traveling headvelocity 606 to the sensed traveling head position 730 and the sensedtraveling head velocity 732 values. The output of the twenty-firstsummation junction 746 may also be viewed as the estimated travelinghead disturbance force term 644, an estimate of the un-modeleddisturbances acting on the traveling head physical system. In somecontexts, the estimated traveling head disturbance force term 644 may bereferred to as an estimated disturbance force feedback value that is asmoothed and based on actuator position sensor information.

A twenty-second summation junction 750 sums the output of thetwenty-first summation junction 746, the observer feed forward travelinghead force command 643, an estimated traveling head weight 752, thenegative of the output of the estimated traveling head frictioncomponent 760, and the negative of the output of the estimated travelinghead damping gain 762. The effect of the summation of the output of thetwenty-first summation junction 746, the observer feed forward travelinghead force command 643, the estimated traveling head weight 752, thenegative of the output of the estimated traveling head frictioncomponent 760, and the negative of the output of the estimated travelinghead damping gain 762 is to produce through the model a filteredvelocity and position related value that is zero time lagged or zerophase lagged with respect to the sensed traveling head position 730 andthe sensed traveling head velocity 732.

The estimated traveling head friction component 760 and the estimatedtraveling head damping gain 762 are provided to take into accountfriction and damping effects that may be present in the mechanicalstructure associated with the hydraulic actuators 110-a, b, for examplemechanical rails or guides which substantially constrain the hydraulicactuators 110-a, b to motion in a single Z-axis. The estimated travelinghead friction component 760 is a function of the polarity of theestimated traveling head velocity 758. The damping effect is modeled asthe estimated traveling head velocity 758 amplified by the estimatedtraveling head damping gain 762. In combination with the presentdisclosure, the estimated traveling head damping gain 762 and theestimated traveling head friction component 760 may be determined and/ortuned by one skilled in the art by collecting data during experimentaloperation of the control system and fitting the traveling head model tothe data. The value of the estimated traveling head weight 752 may bedetermined by weighing the traveling head 156, 160, by taking the netweight identified on a specification provided by a manufacturer of thetraveling head 156, 160, or by some other known manner. The output ofthe twenty-second summation junction 750 corresponds to a force term.The output of the twenty-second summation junction 750 is amplified byan inverse estimated traveling head mass gain 766. The value of theinverse estimated traveling head mass gain 766 is inversely proportionalto the mass of the traveling head, and the mass of the traveling head156, 160 may be determined from the weight of the traveling head 156,160.

The output of the inverse estimated traveling head mass gain 766 is anacceleration term. The output of the inverse traveling head mass gain766 is integrated by an eighth integrator 768. The output of the eighthintegrator 768 is a velocity term, the estimated traveling head velocity606, because generally the integration of an acceleration produces avelocity. The output of the eighth integrator 768 is integrated by aninth integrator 770. The output of the ninth integrator 770 is aposition term, the estimated traveling head position 610, becausegenerally the integration of a velocity produces a position.

In some contexts, the estimated traveling head weight 752, the estimatedtraveling head friction component 760, the estimated traveling headdamping gain, and inverse traveling head mass gain 766 may be referredto as a model of the traveling head 156, 160, as a model of thetraveling head 156, 160 and associated slip bowl 154, 158, or as a modelof a force coupling component. In some contexts, the traveling head 156,160 may be referred to as a force coupling component, e.g., a forcecoupling component that couples the force output by the actuators 110 toone of the slip bowl 154, 158. In some cases the model of the travelinghead 156, 160 may take into account or include the slip bowl 154, 158.In some contexts, the estimated traveling head friction component 760may be referred to as a force coupling friction component, the estimatedtraveling head weight 752 may be referred to as an estimated weight ofthe force coupling component, the estimated traveling head damping gainmay be referred to as an estimated damping factor of the force couplingcomponent, and the inverse traveling head mass gain 766 may beassociated with an estimated mass of the force coupling component.

Turning now to FIG. 13, an embodiment of a work string controller 800 isdiscussed. The work string controller 800 is one embodiment of thesystem controller 10 of the control system architecture 8 described withreference to FIG. 1. The work string controller 800 is configured tocontrol one or more manipulator control systems 300, for example a firstmanipulator control system 300-a, a second manipulator control system300-b, and a third manipulator control system 300-c, whereby to controlthe work string 152. In an embodiment, the work string controller 800controls the work string 152 through controlling the dual-jacking system150. In this embodiment, the first manipulator control system 300-acontrols the first and second hydraulic actuators 110-a, b and the firstslip bowl 154, the second manipulator control system 300-b controls thethird and fourth hydraulic actuators 110-c, d and the second slip bowl158, and the third manipulator control system 300-b controls the thirdor stationary slip bowl 162. In another embodiment, the work stringcontroller 800 may control the work string 152 by another means, forexample using more than two pairs of hydraulic actuators 110 or forexample by using a different kind of actuator. In an embodiment, thework string controller 800 comprises a simulated force feedback section802, a model controller 804, and a manipulator commands generator 806.

The work string controller 800 receives commanded work string values,for example a work string position command 818 and a work stringvelocity command 828, as control inputs. These commanded work stringvalues 818, 828 may come from a user interface or an operator controlstation. The work string controller 800 also receives a plurality ofsensed and commanded values from components that are part of the controlsystem architecture 8. The work string controller 800 receives sensed orestimated values of manipulator position Z_(TH1), Z_(TH2) andmanipulator velocity V_(TH1), V_(TH2), for example from the travelinghead position sensors 314 a, b, the traveling head velocity sensors 316a, b or from the traveling head position and velocity observer 328. Thework string controller 800 receives state value of slip bowls S_(SB1),S_(SB2), S_(SB3) from the slip bowls 154, 158, 162. The sensed orestimated values of position and velocity and of slip bowl state may beconsidered to be feedback to the work string controller 800 from themanipulator physical systems. The work string controller 800 outputscommanded values of manipulator position Z_(TH1)*, Z_(TH2)*, manipulatorvelocity V_(TH1)*, V_(TH2)*, manipulator acceleration A_(TH1)*,A_(TH2)*, workstring force F_(WS/TH1)*, F_(WS/TH2)*, and slip bowl stateS_(SB1)*, S_(SB2)*, S_(SB3)*, for example to the traveling headcontroller 326 and to the slip bowl 154. At a high level, the workstring controller 800 takes into account the command inputs and thefeedback inputs to develop commands that are output to the manipulatorcontrollers 300.

In an embodiment, the simulated force feedback section 802 comprisesthree manipulator simulated force feedback components 810: a firstmanipulator simulated force feedback component 810-a associated with theactuators 110-a, b and the first slip bowl 154, a second manipulatorsimulated force feedback component 810-b associated with the actuators110-c, d and second slip bowl 158, and a third simulated force feedbackcomponent 810-c associated with the stationary slip bowl 162. The firstmanipulator simulated force feedback component 810-a receives sensed orestimated first traveling head position, commanded first traveling headposition, sensed or estimated first traveling head velocity, commandedfirst traveling head velocity, sensed or estimated first slip bowlposition and commanded first slip bowl position inputs and generatestherefrom a simulated force feedback of the work string on the firstmanipulator 812-a. The second manipulator simulated force feedbackcomponent 810-b receives sensed or estimated second traveling headposition, commanded second traveling head position, sensed or estimatedsecond traveling head velocity, commanded second traveling headvelocity, sensed or estimated second slip bowl position, and commandedsecond slip bowl position inputs and generates therefrom a simulatedforce feedback of the work string on the second manipulator 812-b. Thethird manipulator simulated force feedback component 810-c receives asensed or estimated stationary slip bowl position and a commandedstationary slip bowl position as inputs and generates therefrom asimulated force feedback of the work string on the third manipulator812-c. A twenty-third summation junction 814 sums the simulated forcefeedback of the work string on the first, second, and third manipulator812-a, b, c to determine a combined simulated force feedback of the workstring on the manipulators 812.

The model controller 804 comprises a PID controller section and a workstring model section. The intention of the model controller 804 is toproduce an estimated work string position 840 and an estimated workstring velocity 842.

The estimated work string position 840 is negatively summed with thework string position command 818 by a twenty-fourth summation junction820 to produce a position error term. The estimated work string position840 provides a negative feedback term. The output of the twenty-fourthsummation junction 820 is amplified by a seventh proportional gain 821.The output of the twenty-fourth summation junction 820 is integrated bya tenth integrator 822 and amplified by a sixth integral gain 823. Inanother embodiment, the output of the twenty-fourth summation junction820 may be first amplified by the sixth integral gain 823 and thenintegrated by the tenth integrator 822. The estimated work stringvelocity 842 is negatively summed with the work string velocity command828 by a twenty-fifth summation junction 830 to produce a velocity errorterm. The estimated work string velocity 842 provides a negativefeedback term. The output of the twenty-fifth summation junction 830 isamplified by a third derivative gain 831. The processing of the velocityterm is considered to be a derivative component with respect to the workstring position because generally velocity is the derivative ofposition. The output of the twenty-third summation junction 814 isnegatively summed with the output of the seventh proportional gain 821,the output of the sixth integral gain 823, and the output of the thirdderivative gain 831 by a twenty-sixth summation junction 832. The outputof the twenty-third summation junction 814 effectively couples positionand velocity feedback, in the form of simulated force feedback of thework string on the manipulators 812, from the manipulators into theestimation of work string position and velocity. In an embodiment, thegeneral intention is that if one of the manipulators is not achievingthe targeted manipulator position, the simulated force feedback termgrows large, and the position commands to the other non-laggingmanipulators are adapted accordingly. This may promote bettersynchronization among manipulators when a heavy load or an operationalanomaly occurs.

In another embodiment, sensed values of work string position and workstring velocity may be fed directly to the manipulator commandsgenerator 802. Alternatively, in another embodiment, a sensed value ofthe work string position and work string velocity may be available, thesensed value of work string position may be substituted for theestimated work string position 840 input to the twenty-fourth summationjunction 820, and the sensed value of work string velocity may besubstituted for the estimated work string velocity 842 input to thetwenty-fifth summation junction 830.

The output of the twenty-sixth summation junction 832 is amplified by amodel gain 834. The model gain 834 is inversely proportional to theestimated mass of the work string. During well bore servicing operationsthe mass of the work string may change, for example as joints of pipeare added to or removed from the work string, and in an embodiment, themodel gain 834 may be a changing value rather than a static value. Inanother embodiment, however, the model gain 834 may be set to a staticvalue associated with a static estimated mass of the work string. Theoutput of the model gain 834 is integrated by an eleventh integrator 836to produce the estimated work string velocity 842. The output of theeleventh integrator 836 is integrated by a twelfth integrator 838 toproduce the estimated work string position 840.

In an embodiment, the manipulator commands generators 806 may beselected to operate in a plurality of operation modes for controllingthe first, second, and third manipulators cooperatively. A first modemay be a distributed load or high capacity sequential mode, where thefirst and second manipulators are controlled to concurrently grip thework string 152 and to apply substantially equal force to the workstring 152 in the same direction at the same time. A second mode may bea high speed sequential mode, where the first and second manipulatorstrade off gripping the work string 152 and applying force to the workstring 152 in a sequence of start and stop motions. The high speedsequential mode could also be extended to include all threemanipulators. A third mode may be a high speed continuous mode, wherethe first and second manipulators trade off gripping the work string 152and applying force to the work string 152 in a manner which constrainswork string motions to substantially constant work string velocity orsubstantially constant work string acceleration or decelerationindependent of manipulator trajectories. A fourth mode may be a highspeed constrained mode, where the first and second manipulators tradeoff gripping the work string 152 and applying force to the work string152 in a manner which is constrained by a maximum hand-off speed betweenthe manipulators. In other embodiments with multiple manipulators andconstraints, combinations of these modes are contemplated by the presentdisclosure. A user interface (not shown), for example a control panel,may be used to select the operation mode of the manipulator commandsgenerator 806 and to input the work string position command 818 and thework string velocity command 828. In another embodiment, the mode ofoperation may be chosen automatically as the system conditions change,including but not restricted to the changing weight of the work string152. In response to the operation mode selection, the estimated workstring position 840, and the estimated work string velocity 842, themanipulator commands generators 806 may employ an internal map or tableor program to generate the operation mode specific manipulatorcontroller command input vectors 340. In an embodiment, a pipe collarindication 844, which may be provided by a collar locator such as thatshown in FIG. 16, is also input to the manipulator commands generator806. The manipulator commands generator 806 may employ the pipe collarindication 844 to avoid commanding the first and second slip bowls 154,158 and the stationary slip bowl 162 to close on a pipe collar, asituation which would prevent the first and second slip bowls 154, 158and the stationary slip bowl 162 from closing and gripping the workstring 152 securely.

The manipulator commands generator 806 generates the first slip bowlcommand 214, the first traveling head velocity command 502-a, the firsttraveling head position command 602-a, the first traveling headacceleration command 634-a, a first feed forward work string loadcommand 632-a, the second slip bowl command 220, the second travelinghead velocity command 502-b, the second traveling head position command602-b, the second traveling head acceleration command 634-b, a secondfeed forward work string load command 632-b, and the stationary slipbowl command 228.

Turning now to FIG. 14, an exemplary manipulator force feedbackcomponent 810 is discussed. The manipulator force feedback component 810comprises a PID controller section, a slip bowl model section, and aslip bowl model PI controller section. The sensed traveling headposition 730 is negatively summed with the commanded traveling headposition 602 by a twenty-seventh summation junction 860 to produce aposition error term. The sensed traveling head position 730 provides anegative feedback term. The output of the twenty-seventh summationjunction 860 is amplified by an eighth proportional gain 861. The outputof the twenty-eighth summation junction 860 is integrated by athirteenth integrator 862 and amplified by a seventh integral gain 863.In another embodiment, the output of the twenty-eighth summationjunction 860 may be first amplified by the seventh integral gain 863 andthen may be integrated by the thirteenth integrator 862. The sensedtraveling head velocity 732 is negatively summed with the commandedtraveling head velocity 502 by a twenty-eighth summation junction 864 toproduce a velocity error term. The sensed traveling head velocity 732provides a negative feedback term. The output of the twenty-eighthsummation junction 864 is amplified by a fourth derivative gain 865. Theprocessing of the traveling head velocity term is considered to be aderivative component with respect to the traveling head position becausegenerally velocity is the derivative of position. The output of theeighth proportional gain 861, the seventh integral gain, and the fourthderivative gain 865 are summed by a twenty-ninth summation junction 866to produce an estimated work string force feedback on the traveling head867. In combination with the present disclosure, the values of theeighth proportional gain 861, the seventh integral gain 863, and thefourth derivative gain 864 may be readily determined by one skilled inthe control systems art.

The slip bowl command 214, 220, 226 is processed by a slip bowl model870 to produce an estimated slip bowl position 871. In an embodiment,the slip bowl model 870 may comprise a simple time delay to model thetime it takes for the physical slip bowl system to follow the slip bowlcommand under normal situations. In another embodiment, the sensed slipbowl position and the slip bowl command 214, 220, 226 may relate to acontinuous slip bowl position from being fully disengaged to being fullyengaged, where the slip bowl model 870 may become unnecessary. Thesensed slip bowl position 216 is negatively summed with the estimatedslip bowl state 871 by a thirtieth summation junction 872. The output ofthe thirtieth summation junction 872 is amplified by a ninthproportional gain 876. The output of the thirtieth summation junction872 is integrated by a fourteenth integrator 877 and amplified by aneighth integral gain 878. In another embodiment, the output of thethirtieth summation junction 872 may first be amplified by the eighthintegral gain 878 and then integrated by the fourteenth integrator 877.The output of the ninth proportional gain 876 and the output of theeighth integral gain 878 are summed by a thirty-first summation junction879 to produce an estimated work string force feedback on the slip bowl.In an embodiment, the value of the eighth integral gain 878 may be setto a substantially higher value than that of the seventh integral gain863, so the estimated work string force feedback on the slip bowl mayramp up more rapidly than the estimated work string force feedback onthe traveling head. In an embodiment, the eighth integral gain 878 maybe about five times larger than the seventh integral gain 863. Inanother embodiment, the eighth integral gain 878 may be about ten timeslarger than the seventh integral gain 863. In yet another embodiment,the eighth integral gain 878 may be about fifty times larger than theseventh integral gain 863. For example, if the physical slip bowl systemdoes not follow the estimated slip bowl state, for example if the slipbowl 154, 158, 162 does not close because it has erroneously attemptedto close on a pipe collar, it is desirable for the estimated work stringforce feedback on the slip bowl to rapidly increase in value to causethe several manipulators to come to a stop or even reverse directionmomentarily. In combination with the present disclosure, the values ofthe ninth proportional gain 876 and the eighth integral gain 878 may bereadily determined by one skilled in the control systems art.

The output of the twenty-ninth summation junction 866 and thethirty-first summation junction 879 are summed by a thirty-secondsummation junction 884 to determine a simulated force feedback of thework string on the manipulator.

The proportional, integral, and derivative gains in the several controlcomponents described above may be determined by an initial calculationbased on a pole-zero system stability analysis and a frequency responseanalysis of the control system and later the gains may be furtheradjusted when deploying the control system to actual use. The generaldesign approach is to design the control system based on a frequencydomain mathematical model, for example expressed using Laplacetransforms. This mathematical model includes both control elements andphysical elements of the control system. The manipulator control system300 and the work string controller 800 controlling two or moremanipulator control systems 300 may be implemented as hierarchicalcontrol systems, wherein the control feedback loops are closed and tunedin order from the lowest level or innermost loop to the highest level oroutermost loop. The gains at each level may be tuned to the fastestfrequency response which can be attained while maintaining a stablesystem with good disturbance rejection. In a work string controllersystem such as that disclosed herein, large disturbances are possible,for example large manipulator force transients associated with portionsof the well bore collapsing in on the work string 152 and increasing thefriction experienced by the work string 152 moving in the well bore.Therefore, it may be prudent to employ reasonable safety factors insetting the design values for disturbances that may be experienced whentuning the control gains. According to a generally accepted practice,when control loops are placed around other control loops, as is the casewith the work string controller 800 and the manipulator control system300, the outer loop gains may be designed to achieve about one quarterthe frequency response of the next lower control loop. In someembodiments, however, this general practice may not be adhered to.

While the figures illustrate the control components in terms of theLaplace transform, which is a continuous time transform, one skilled inthe control systems art could readily adapt the continuous timeillustrations to discrete time illustrations. The principal modificationwould be replacing the continuous time Laplace transform of theintegration operation, represented as 1/S in the several integratorblocks, by T_(s)/(Z−1), where Ts is a constant proportional to thecontrol system data sampling interval and 1/(Z−1) is the discrete timeZ-transform of the integration operation.

As would be appreciated by those of ordinary skill in the controlsystems art, some portions of the above described control systemcomponents may be combined or separated without materially altering thefunction of the control system. For example, other combinations ofsummation junctions may be employed to build the flow regulator 320without materially changing the control function of the flow regulator320. For example, in another embodiment, the summation provided by thesecond summation junction 416 and the third summation junction 420 maybe performed by a single summation junction without materially alteringthe control function of the flow regulator 320. Additionally, the orderof some portions of the above described control components may bechanged without materially changing the function of the control system.For example, reversing the positions of the first integrator 412 withthe first integral gain 414 in the flow regulator 320 may not materiallyalter the function of the flow regulator 320. All such trivialcombinations and positional rearrangements that do not materially alterthe control function of the controllers and control components describedabove are contemplated by this disclosure.

Turning now to FIG. 15, some kinematic parameters associated with atwelve stage traveling head trajectory are illustrated. The illustratedkinematic parameters provide one possible model of kinematic parametersassociated with the control system architecture 8 depicted in FIG. 1,for example kinematic parameters associated with the dual-jacking system150 depicted in FIG. 3. The kinematic equations disclosed below,including equation (1) through equation (48), provide exemplarykinematic equations that may be employed by the manipulator commandsgenerators 806 in part to generate the manipulator commands in one modeof operation, for example in a high speed continuous mode of operation.In other modes of operation, other kinematic parameters and otherkinematic equations may apply. In combination with the presentdisclosure, one skilled in the art may make appropriate modificationsand extensions of these kinematic parameters and associated kinematicequations to apply this information to other related control systemsand/or manipulator systems. Table 1 identifies some trajectory stagelengths and describes the stages. Table 2 identifies some trajectoryparameters.

TABLE 1 Trajectory Stage Lengths L₁ 0 in Stage 1 - Maximum Accelerationto Match Pipe Speed L₂ ? Stage 2 - Slip Bow Engagement (Hand Off) forFully Loaded Single L₃ ? Stage 3 - Accelerate for Hand Off L₄ ? Stage4 - Relative Jack Velocity for Slip Bowl Disengagement (Hand L₅ ? Stage5 - Accelerate Away from Pipe L₆ ? Stage 6 - Potential Maximum VelocityAchieved L₇ ? Stage 7 - Decelerate for Return Stroke L₈ L_(s) Stage 8 -Zero Velocity Dwell for Directional Valve Switch L₉ L_(s) Stage 9 -Maximum Acceleration on Return Stroke L₁₀ ? Stage 10 - Potential MaximumVelocity Achieved L₁₁ ? Stage 11 - Maximum Deceleration on Return StrokeL₁₂ 0 in Zero Velocity Dwell for Directional Valve Switch

TABLE 2 Trajectory Parameters D_(HO) ? Hand Off Length D_(SJ) ? FullyLoaded Single Jack Portion of Stroke Length D_(SB) ? Distance Traveledduring Slip Bowl Response Time t_(SB) D_(slip) 1 in Relative Distancefor Slip Bowl Disengagement w.r.t. Pipe F_(s) 6 Slip Insurance SafetyFactor (Shutdown Conditional) Q_(max) 60 Maximum Output Flow rate perPump GPM

Maximum Output Flow Rate of Change per Pump V_(dn) ? Maximum AchievableVelocity Downward V_(up) ? Maximum Achievable Velocity Upward A_(dn) ?Maximum Achievable Acceleration Downward A_(up) ? Maximum AchievableAcceleration Upward

$\begin{matrix}{v_{1} = 0} & (1) \\{L_{1} = 0} & (2) \\{{L_{2} - L_{1}} = {\frac{1}{2}a_{1}t_{1}^{2}}} & (3) \\{v_{2} = {a_{1}t_{1}}} & (4) \\{v_{2} = v_{P}} & (5) \\{a_{2} = 0} & (6) \\{{L_{3} - L_{2}} = {D_{SJ} + D_{HO} + D_{SB}}} & (7) \\{{L_{3} - L_{2}} = {v_{2}t_{2}}} & (8) \\{{L_{5} - L_{3}} = D_{HO}} & (9) \\{v_{3} = v_{2}} & (10) \\{{L_{4} - L_{3}} = {{v_{3}t_{3}} + {\frac{1}{2}a_{3}t_{3}^{2}}}} & (11) \\{v_{4} = {v_{3} + {a_{3}t_{3}}}} & (12) \\{a_{3} = a_{DN\_ MAX}} & (13) \\{D_{slip} = {\left( {L_{5} - L_{3}} \right) - {v_{P}\left( {t_{3} + t_{4}} \right)}}} & (14) \\{{L_{5} - L_{4}} = {v_{4}t_{4}}} & (15) \\{a_{4} = 0} & (16) \\{v_{5} = v_{4}} & (17) \\{{L_{6} - L_{5}} = {{v_{5}t_{5}} + {\frac{1}{2}a_{5}t_{5}^{2}}}} & (18) \\{{L_{6} - L_{5}} = {D_{slip}F_{s}}} & (19) \\{v_{6} = {v_{5} + {a_{5}t_{5}}}} & (20) \\{t_{6} = 0} & (21) \\{a_{6} = 0} & (22) \\{L_{7} = L_{6}} & (23) \\{L_{2} = {L_{8} - L_{5}}} & (24) \\{v_{7} = {a_{7}t_{7}}} & (25) \\{v_{7} = v_{6}} & (26) \\{t_{7} = {NT}_{s}} & (27) \\{{L_{8} - L_{7}} = {{v_{7}t_{7}} - {\frac{1}{2}a_{7}t_{7}^{2}}}} & (28) \\{v_{8} = 0} & (29) \\{a_{8} = 0} & (30) \\{t_{8} = T_{switch}} & (31) \\{v_{9} = 0} & (32) \\{v_{10} = {a_{9}t_{9}}} & (33) \\{v_{10} = {- v_{UP\_ MAX}}} & (34) \\{a_{9} = {- a_{UP\_ MAX}}} & (35) \\{L_{9} = L_{8}} & (36) \\{{L_{10} - L_{9}} = {\frac{1}{2}a_{9}t_{9}^{2}}} & (37) \\{{L_{11} - L_{10}} = {v_{10}t_{10}}} & (38) \\{L_{11} = {L_{8} - L_{10}}} & (39) \\{a_{10} = 0} & (40) \\{v_{11} = v_{UP\_ MAX}} & (41) \\{t_{11} = t_{9}} & (42) \\{a_{11} = a_{UP\_ MAX}} & (43) \\{v_{12} = 0} & (44) \\{t_{12} = T_{switch}} & (45) \\{a_{12} = 0} & (46) \\{L_{12} = 0} & (47) \\{t_{2} = {t_{1} + t_{3} + t_{4} + t_{5} + t_{6} + t_{7} + t_{8} + t_{9} + t_{10} + t_{11} + t_{12}}} & (48)\end{matrix}$

Unknowns:

L₁, L₂, L₃, L₄, L₅, L₆, L₇, L₈, L₉, L₁₀, L₁₁, L₁₂

t₁, t₂, t₃, t₄, t₅, t₆, t₇, t₈, t₉, t₁₀, t₁₁, t₁₂

v₁, v₂, v₃, v₄, v₅, v₆, v₇, v₈, v₉, v₁₀, v₁₁, v₁₂

a₁, a₂, a₃, a₄, a₅, a₆, a₇, a₈, a₉, a₁₀, a₁₁, a₁₂

Turning now to FIG. 16, an embodiment of a collar locater 900 isdescribed. In an embodiment, the collar locator 900 comprises a firstdigital camera 908, a first light source 914, a second digital camera918, a second light source 920, and a collar detector 922. The workstring 152 includes a first collar 902 and a second collar 904. Collarsin the work string 152 may be formed where two ends of pipes arethreaded into each other. The collars 902 and 904 have a larger diameterand a broader profile than the rest of the pipe sections when viewed bythe first and second digital cameras 908, 918. The first and seconddigital cameras 908, 918 provide images of the work string 152 to thecollar detector 922 which processes these images to identify collars.The collar detector 922 outputs a collar indication 844. In anembodiment, the collar indication 844 may indicate when a collar is inview of the first digital camera 908, when a collar is in view of thesecond digital camera 918, and/or the estimated position of one or morecollars.

In an embodiment, the digital image of a section of the work string 152may be thresholded by the collar detector 922 to distinguish the workstring 152 from the background. Thresholding is an image processingtechnique that designates pixels as object pixels or background pixelsbased on comparing the value of the pixels to a threshold value, forexample a grayscale value. In different embodiments, object pixels maybe either lighter or darker than the threshold value. Afterthresholding, an edge detection computer vision algorithm may be appliedby the collar detector 922 to determine the approximate width of theprofile of the portion of the work string 152 within the image. If thewidth of the work string 152 exceeds a limit, the collar detector 922determines that a collar is in the image.

In an embodiment, the first and second digital cameras 908, and 918 maycapture images of the work string 152 at a sample rate of 30 times persecond or greater. In this embodiment, the collar locator 900 may beable to determine a speed of the work string 152 and to provide anestimate of the location of the first collar 902 and the second collar904 after they have passed out of the view field of the first and seconddigital cameras 908, 918 based on the calculated work string velocity.

Turning now to FIG. 17, a method 950 of controlling the work string 152is described. In block 951, the work string is placed in a well bore. Inblock 952, a work string trajectory input is received. The work stringtrajectory characterizes a desired motion of the work string 152 as oneor more linked pairs of position and velocity, or work string targetposition and work string velocity target. These may be referred to as anordered sequence of target pairs, wherein each target pair comprises awork string target position and a work string target velocity. In afirst example, the work string trajectory input may include one linkedpair of position and velocity having a position target of 5000 feet anda velocity target of 5 feet per second. In a second example, the workstring trajectory input may include six linked pairs of position andvelocity—a first position target of 5010 feet and a first velocitytarget of 5 feet per second, a second position target of 4990 feet and asecond velocity target of −20 feet per second, a third position targetof 5010 feet and a third velocity target of 20 feet per second, a fourthposition target of 4990 feet and a fourth velocity target of −20 feetper second, a fifth position target of 5010 feet and a fifth velocitytarget of 20 feet per second, and a sixth position target of 0 feet anda sixth velocity target of −5 feet per second. This second examplecorresponds to lowering the work string 152 into the well bore to adepth of about 5000 feet and oscillating the work string 152 partiallyin and out of the well bore and then retracting the work string 152 outof the well bore. It will readily be appreciated that a wide variety ofwork string manipulation regimes may be described and/or defined by sucha series of linked pairs of position and velocity, all of which arecontemplated by the present disclosure.

In block 954, the simulated force feedback of the work string on themanipulators is determined. The simulated force feedback of the workstring on the manipulators is the sum of the simulated force feedback ofthe work string on each of the manipulators of the control system. In anembodiment, three manipulators are deployed, for example thedual-jacking system 150, where the first traveling head 156 and thefirst slip bowl 154 comprise a first manipulator, the second travelinghead 160 and the second slip bowl 158 comprise a second manipulator, andthe stationary slip bowl 162 comprises a third manipulator. In thisembodiment, the simulated force feedback of the work string on the firstmanipulator 812-a, the simulated force feedback of the work string onthe second manipulator 812-b, and the simulated force feedback of thework string on the third manipulator 812-c are determined and summed.

In block 956, the estimated work string velocity 842 and the estimatedwork string position 840 are determined. In an embodiment, a model forceis determined based on the estimated feedback force of the manipulatorson the work string 812, on the work string position command 818, and onthe work string velocity command 828. The model force is multiplied bythe reciprocal of the estimated work string mass to transform the modelforce to a model work string acceleration. The estimated work stringvelocity 842 is determined by integrating the model work stringacceleration. The estimated work string position 840 is determined byintegrating the estimated work string velocity 842.

In block 958, a first manipulator controller command input vector 340-ais determined based on the estimated work string velocity 842, theestimated work string position 840, the pipe collar indication 844, andthe mode of operation. The first manipulator controller command inputvector 340-a is transmitted to the first manipulator control system300-a.

In block 960, a second manipulator controller command input vector 340-bis determined based on the estimated work string velocity 842, theestimated work string position 840, the pipe collar indication 844, andthe mode of operation. The second manipulator controller command inputvector 340-b is transmitted to the second manipulator control system300-b.

In block 962, a first manipulator position command and a firstmanipulator velocity command are determined by using the firstmanipulator controller command input vector 340-a to drive the firstmanipulator physical system components to desired values.

In block 964, a second manipulator position command and a secondmanipulator velocity command are determined by using the secondmanipulator controller command input vector 340-b to drive the secondmanipulator physical system components to desired values. In block 966,the first and second manipulators are automatically controlled based onthe first and second manipulator position and velocity commands. Themethod 950 then ends or may be repeated at a periodic rate effective tocontrol the work string 152.

The system described above may be implemented on any general-purposecomputer with sufficient processing power, memory resources, and networkthroughput capability to handle the necessary workload placed upon it.FIG. 18 illustrates a typical, general-purpose computer system suitablefor implementing one or more embodiments disclosed herein. The computersystem 1080 includes a processor 1082 (which may be referred to as acentral processor unit or CPU) that is in communication with memorydevices including secondary storage 1084, read only memory (ROM) 1086,random access memory (RAM) 1088, input/output (I/O) devices 1090, andnetwork connectivity devices 1092. The processor may be implemented asone or more CPU chips.

The secondary storage 1084 is typically comprised of one or more diskdrives or tape drives and is used for non-volatile storage of data andas an over-flow data storage device if RAM 1088 is not large enough tohold all working data. Secondary storage 1084 may be used to storeprograms which are loaded into RAM 1088 when such programs are selectedfor execution. The ROM 1086 is used to store instructions and perhapsdata which are read during program execution. ROM 1086 is a non-volatilememory device which typically has a small memory capacity relative tothe larger memory capacity of secondary storage. The RAM 1088 is used tostore volatile data and perhaps to store instructions. Access to bothROM 1086 and RAM 1088 is typically faster than to secondary storage1084.

I/O devices 1090 may include printers, video monitors, liquid crystaldisplays (LCDs), touch screen displays, keyboards, keypads, switches,dials, mice, track balls, voice recognizers, card readers, paper tapereaders, or other well-known input devices.

The network connectivity devices 1092 may take the form of modems, modembanks, ethernet cards, universal serial bus (USB) interface cards,serial interfaces, token ring cards, fiber distributed data interface(FDDI) cards, wireless local area network (WLAN) cards, radiotransceiver cards such as code division multiple access (CDMA) and/orglobal system for mobile communications (GSM) radio transceiver cards,and other well-known network devices. These network connectivity devices1092 may enable the processor 1082 to communicate with an Internet orone or more intranets. With such a network connection, it iscontemplated that the processor 1082 might receive information from thenetwork, or might output information to the network in the course ofperforming the above-described method steps. Such information, which isoften represented as a sequence of instructions to be executed usingprocessor 1082, may be received from and outputted to the network, forexample, in the form of a computer data signal embodied in a carrierwave. In an embodiment, portions of the control system 8, the controller202, the manipulator control system 300, and/or the work stringcontroller 800 may be reconfigured and/or gains be tuned from a remotecomputer via the network connectivity devices 1092.

Such information, which may include data or instructions to be executedusing processor 1082 for example, may be received from and outputted tothe network, for example, in the form of a computer data baseband signalor signal embodied in a carrier wave. The baseband signal or signalembodied in the carrier wave generated by the network connectivitydevices 1092 may propagate in or on the surface of electricalconductors, in coaxial cables, in waveguides, in optical media, forexample optical fiber, or in the air or free space. The informationcontained in the baseband signal or signal embedded in the carrier wavemay be ordered according to different sequences, as may be desirable foreither processing or generating the information or transmitting orreceiving the information. The baseband signal or signal embedded in thecarrier wave, or other types of signals currently used or hereafterdeveloped, referred to herein as the transmission medium, may begenerated according to several methods well known to one skilled in thecontrol systems art.

The processor 1082 executes instructions, codes, computer programs,scripts which it accesses from hard disk, floppy disk, optical disk(these various disk based systems may all be considered secondarystorage 1084), ROM 1086, RAM 1088, or the network connectivity devices1092. While only one processor 1092 is shown, multiple processors may bepresent. Thus, while instructions may be discussed as executed by aprocessor, the instructions may be executed simultaneously, serially, orotherwise executed by one or multiple processors.

While several embodiments have been provided in the present disclosure,it should be understood that the disclosed systems and methods may beembodied in many other specific forms without departing from the spiritor scope of the present disclosure. The present examples are to beconsidered as illustrative and not restrictive, and the intention is notto be limited to the details given herein. For example, the variouselements or components may be combined or integrated in another systemor certain features may be omitted or not implemented.

Also, techniques, systems, subsystems, and methods described andillustrated in the various embodiments as discrete or separate may becombined or integrated with other systems, modules, techniques, ormethods without departing from the scope of the present disclosure.Other items shown or discussed as directly coupled or communicating witheach other may be indirectly coupled or communicating through someinterface, device, or intermediate component, whether electrically,mechanically, or otherwise. Other examples of changes, substitutions,and alterations are ascertainable by one skilled in the art and could bemade without departing from the spirit and scope disclosed herein.

1. A mass position and velocity observer, comprising: aproportional-integral-derivative (PID) controller portion operable todetermine a mass position error and a mass velocity error and togenerate a corrective signal based on the mass position error and on themass velocity error; a first gain operable to amplify an indication ofmass velocity by a mass damper gain to generate a damper force signal; aforce summation portion that is operable to determine a summed forceterm based on the corrective signal, based on the damper force signal,based on a force command, and based on a mass weight term; a second gainoperable to amplify the summed force term by an inverse mass gain and togenerate a mass acceleration term; a first integrator operable tointegrate the mass acceleration term to generate a mass velocity termand to output an estimate of mass velocity; and a second integratoroperable to integrate the mass velocity term to generate a mass positionterm and to output an estimate of mass position.
 2. The mass positionand velocity observer of claim 1, wherein theproportional-integral-derivative controller portion is further operableto produce a mass force disturbance term based on the mass positionerror and on the mass velocity error.
 3. The mass position and velocityobserver of claim 1, wherein the mass position error is determined asthe difference of a sensed mass position and the estimate of massposition.
 4. The mass position and velocity observer of claim 1, whereinthe mass velocity error is determined as the difference of a sensed massvelocity and the estimate of mass velocity.
 5. The mass position andvelocity observer of claim 1, further comprising a third gain operableto amplify the indication of mass velocity by a friction gain todetermine a friction force signal, wherein the summed force term isfurther based on the friction force signal.
 6. The mass position andvelocity observer of claim 1, wherein the mass weight term is a constantvalue configured in the mass position and velocity observer.
 7. Acontrol system for controlling movement of a work string in a well bore,comprising: a controller comprising a processor, a memory, and a massvelocity and position observer component comprising aproportional-integral-derivative (PID) controller portion operable todetermine a mass position error and a mass velocity error and togenerate a corrective signal based on the mass position error and on themass velocity error; a first gain operable to amplify an indication ofmass velocity by a mass damper gain to generate a damper force signal; aforce summation portion that is operable to determine a summed forceterm based on the corrective signal, based on the damper force signal,based on a force command, and based on a mass weight term; a second gainoperable to amplify the summed force term by an inverse mass gain and togenerate a mass acceleration term; a first integrator operable tointegrate the mass acceleration term to generate a mass velocity termand to output an estimate of mass velocity; and a second integratoroperable to integrate the mass velocity term to generate a mass positionterm and to output an estimate of mass position, wherein the controllerreceives a work string trajectory input from a user interface, thetrajectory input comprising at least a first work string target positionand a first work string target velocity, and commands a firstmanipulator to move the work string based at least in part on theestimate of mass velocity, the estimate of mass position, and the workstring trajectory input.
 8. The control system of claim 7, wherein theproportional-integral-derivative controller portion is further operableto produce a mass force disturbance term based on the mass positionerror and on the mass velocity error.
 9. The control system of claim 7,wherein the mass position error is determined as the difference of asensed mass position and the estimate of mass position.
 10. The controlsystem of claim 7, wherein the mass velocity error is determined as thedifference of a sensed mass velocity and the estimate of mass velocity.11. The control system of claim 7, further comprising a third gainoperable to amplify the indication of mass velocity by a friction gainto determine a friction force signal, wherein the summed force term isfurther based on the friction force signal.
 12. The control system ofclaim 7, wherein the mass weight term is a constant value configured inthe mass position and velocity observer.
 13. A method of servicing awell bore with a work string, comprising: determining a mass positionerror and a mass velocity error; generating a corrective signal based onthe mass position error and on the mass velocity error; amplifying anindication of mass velocity by a mass damper gain to generate a damperforce signal; determining a summed force term based on the correctivesignal, based on the damper force signal; amplifying the summed forceterm by an inverse mass gain to generate a mass acceleration term;integrating the mass acceleration term to generate a mass velocity termand to output an estimate of mass velocity; integrating the massvelocity term to generate a mass position term and to output an estimateof mass position; receiving a work string trajectory input from a userinterface, the trajectory input comprising at least a first work stringtarget position and a first work string target velocity; and commandinga first manipulator to move the work string based at least in part onthe estimate of mass velocity, the estimate of mass position, and thework string trajectory input.
 14. The method of claim 13, furthercomprising determining a mass force disturbance term based on the massposition error and on the mass velocity error, wherein commanding thefirst manipulator to move the work string is further based on the massforce disturbance term.
 15. The method of claim 13, wherein the massposition error is determined as the difference of a sensed mass positionand the estimate of mass position.
 16. The method of claim 13, whereinthe mass velocity error is determined as the difference of a sensed massvelocity and the estimate of mass velocity.
 17. The method of claim 13,further comprising amplifying the indication of mass velocity by afriction gain to determine a friction force signal, wherein the summedforce term is further based on the friction force signal.
 18. The methodof claim 13, wherein the mass weight term is a constant value.
 19. Themethod of claim 13, wherein determining the summed force term is furtherbased on a force command.
 20. The method of claim 13, whereindetermining the summed force term is further based on a mass weightterm.